Chapter 5
Sexual Dysfunction

The reader may wonder why a book on psychotropic medications has a chapter on sexual dysfunction. There are two reasons:
Broadly speaking, the term "sexual dysfunction" refers to any problem or condition that prevents a satisfactory sex life. It includes any problem, physical or emotional, that prevents an individual or couple from enjoying sexual activity. Since every person is likely to experience transient sexual difficulties on occasion, a sexual problem is considered to be a sexual dysfunction disorder only if it is sustained over time.
Wikipedia (en.wikipedia.org/wiki/Sexual_dysfunction) has the following to say about the different categories of sexual dysfunction.
Sexual dysfunction disorders are generally classified into four categories: sexual desire disorders, sexual arousal disorders, orgasm disorders, and sexual pain disorders.
  1. Sexual desire disorders or decreased libido can be caused by a decrease in normal estrogen (in women) or testosterone (in both men and women) production. Other causes may be aging, fatigue, pregnancy, medications (such as the SSRIs) or psychiatric conditions, such as depression and anxiety.
  2. Sexual arousal disorders were previously known as frigidity in women and impotence in men, though these have now been replaced with less judgmental terms. Impotence is now known as erectile dysfunction, and frigidity has been replaced with a number of terms describing specific problems with, for example, desire or arousal.
    For both men and women, these conditions can manifest as an aversion to, and avoidance of, sexual contact with a partner. In men, there may be partial or complete failure to attain or maintain an erection, or a lack of sexual excitement and pleasure in sexual activity.
    There may be medical causes to these disorders, such as decreased blood flow or lack of vaginal lubrication. Chronic disease can also contribute, as well as the nature of the relationship between the partners. As the success of sildenafil (Viagra) attests, most erectile disorders in men are primarily physical, not psychological conditions.
  3. Orgasm disorders are a persistent delay or absence of orgasm following a normal sexual excitement phase. The disorder can occur in both women and men. Again, the SSRI antidepressants are frequent culprits - these can delay the achievement of orgasm or eliminate it entirely.
  4. Sexual pain disorders affect women almost exclusively and are known as dyspareunia (painful intercourse) and vaginismus (an involuntary spasm of the muscles of the vaginal wall that interferes with intercourse). Dyspareunia may be caused by insufficient lubrication (vaginal dryness) in women.
This chapter addresses the use of prescription medications that may be used to treat some sexual problems. It is not a comprehensive guide to the treatment of sexual dysfunction; in particular, it does not address psychological problems, or sexual pain disorders, for which the reader is advised to look elsewhere. This chapter focuses more narrowly on medical treatment for sexual desire disorder (low libido, also known as Hypoactive Sexual Desire), sexual arousal disorder (such as Erectile Dysfunction, or ED), and orgasm disorder (i.e., Anorgasmia, or difficulty achieving orgasm).
While the primary motivation for this chapter is to address sexual dysfunction caused by psychotropic medications (primarily antidepressants), many of the treatments described are also of value to those whose sexual problems do not arise from medication.

5.1  Solutions for Sexual Dysfunction in General

The solutions described in this section are appropriate for sexual dysfunction in general, meaning whether or not the dysfunction arises from antidepressant medication. While these medications can normally be taken in conjunction with an antidepressant, individual exceptions may occur, and it is important to discuss possible drug interactions with your physician.

5.1.1  Treating Sexual Arousal Disorders

Arousal disorders are most obvious in men, where they take the form of Erectile Dysfunction (ED). ED refers to the inability to develop and sustain an erection, and by definition, refers to men only. Medications that treat ED are available, and the degree to which they work is obvious to the men who take them. These medications have brought great benefit to men who have normal sexual desires, but suffer from ED.
The following sections refer explicitly to ED, rather than arousal disorders in general, because they reflect the language of the prescribing literature for the medications. However, women also experience arousal disorders, although the symptoms are less obvious than those of ED.
Women may experience arousal disorders in the form of dryness or insufficient engorgement, which cause discomfort, and understandable reluctance to engage in sexual activity. Fortunately, the medications (vasodilators) that are useful for ED in men can improve vaginal engorgement and lubrication for women.
Arousal desires in men and women are primarily physical in nature. Psychological problems can certainly lead to arousal problems, but in such cases, the psychological problems are not themselves arousal problems, and must be treated differently.
It is important to realize that medications for arousal disorders are not "aphrodisiacs." They do not help problems of low libido, unlike some other medications described in this chapter.  PDE5 Inhibitors

The big breakthrough in the treatment of ED was the discovery of vasodilators that increase blood flow to the penis. These vasodilators increase the concentration of cyclic guanosine monophosphate (cGMP), a chemical that relaxes the smooth muscles, and increases blood flow to the penis following sexual stimulation. They work by selectively inhibiting a chemical named phosphodiesterase type 5 (PDE5), which destroys cGMP.
The PDE5 inhibitors are very effective medications, with a high success rate. They differ primarily in terms of how quickly their effects are noticed, and how long they last. In all cases, benefits typically are observed in less than an hour. Standard dosing instructions are to take the medication an hour before sexual activity. The benefits may last from a few hours to over a day, depending on the medication and individual variation in response. In general, the longer the half life, the longer the benefits are likely to last.
The most commonly noted side effects are headache and flushing. These effects are rarely serious enough to impair sexual function (or be a health hazard). Excessively prolonged erections (priapism) are unlikely but a possibility, and immediate medical treatment should be sought if erection persists for more than an hour after sexual activity. Prolonged states of erection (lasting more than an hour) can cause serious and irreversible damage to the penis, and are a medical emergency that require immediate treatment.

Warning! Vardenafil has the second-highest risk level (of four) for causing QT Prolongation and serious abnormalities of heart rhythm. Medications at this risk level have been associated with QT Prolongation, but not proven to cause it. The risk for QT Prolongation is not considered high, but medications with lower risk are preferred, especially for anyone who has Long QT Syndrome. If you cannot substitute a medication with lower risk, be alert for heart palpitations. If you experience palpitations, report them to your doctor immediately.

Main Brand Name Chemical Name Chemical Type Half Life Washout Time On-Label Uses Off-Label Uses
Cialis Tadalafil  18 hours 4 days Erectile Dysfunction  
Levitra Vardenafil  5 hours 1 day Erectile Dysfunction  
Viagra Sildenafil  8 hours 2 days Erectile Dysfunction  PGE1 Vasodilators

Another type of vasodilator that is useful for treating ED is the chemical prostaglandin E1 (PGE1), which occurs naturally in the body. An increase in PGE1 concentration in the penis relaxes the smooth muscles, and increases blood flow to the penis following sexual stimulation.
When used to treat ED, PGE1 is supplied in the form of a very small urethral suppository. The half-life is very short, so the medication should be used immediately before sexual activity. Benefits are observed in 5-10 minutes, and last for 30-60 minutes.
The most common side effect is pain in the penis, urethra, or testicles, which is usually mild and temporary.

Main Brand Name Chemical Name Chemical Type Half Life Washout Time On-Label Uses Off-Label Uses
Muse Alprostadil  5 minutes 25 minutes Erectile Dysfunction  Apomorphine

Apomorphine is a dopamine agonist used to treat Parkinson's disease (as Apokyn, an injectable medication) and ED (as Uprima, in sub-lingual tablet form). Unlike vasodilators, Apomorphine stimulates dopamine receptors in the brain. Thus Apomorphine can provide a boost in libido which, in turn, promotes erection. Apomorphine may be useful in situations where vasodilators are not, and vice versa.
Apomorphine is administered by sub-lingual table or injection. The half-life is short, so it should be taken thirty minutes before sexual activity. Benefits are normally observed within 10-20 minutes, and may last for a few hours.
The most common side effect of Apomorphine is nausea.

Main Brand Name Chemical Name Chemical Type Half Life Washout Time On-Label Uses Off-Label Uses
Uprima Apomorphine  40 minutes 4 hours Parkinson's Disease Erectile Dysfunction

Although Apomorphine may be useful for ED, it is not clear that it is more effective for this purpose than other dopamine agonists. The sub-lingual administration and rapid onset of effect are convenient when compared to the vasodilators, but the short half life means that the benefits are not sustained. This may not seem like a problem relative to the vasodilators, but other dopamine agonists have much longer half lives, and may provide the same benefits as Apomorphine on a sustained, rather than intermittent, basis.
The reason Apomorphine is listed separately here, rather than being grouped with the other dopamine agonists, is because the Uprima formulation has been developed specifically for the treatment of Erectile Dysfunction, and because it is too short-lived to be of much use for the treatment of depression. However, it is entirely possible that dopamine agonists with longer half-lives will prove more beneficial for both ED and libido problems. (See Section  Yohimbine

Yohimbine is a prescription medication derived from the Yohimbe tree. It is an a-adrenergic antagonist, meaning it blocks a (alpha) norepinephrine receptors. Yohimbine also has monoamine-oxidase inhibitory effects, and may cause a dangerous increase in blood pressure in conjunction with other medications, or foods that contain tyramine (see www.inchem.org/documents/pims/pharm/yohimbin.htm, or Section, for details).
Yohimbine has multiple effects on the body. It is a stimulant, and increases heart rate and blood pressure. Like all stimulants, Yohimbine may increase anxiety.
Yohimbine is not a vasodilator, but has similar benefits to the vasodilators for ED: it increases blood flow to the penis, and promotes erection. The rapid absorption (about 10 minutes) and short half-life means that Yohimbine should be taken immediately before sexual activity.
The most common side effects of Yohimbine are nausea, shakiness, tension, and anxiety. Overdoses can produce unconsciousness, dizziness, confusion. Excessively prolonged erections (priapism) are unlikely but a possibility, and immediate medical treatment should be sought if erection persists for more than an hour after sexual activity. Prolonged states of erection (lasting more than an hour) can cause serious and irreversible damage to the penis, and are a medical emergency that require immediate treatment.
Given Yohimbine's complex behavior, it is not a first choice for the treatment of ED, but may be useful if other medications prove ineffective.

Main Brand Name Chemical Name Chemical Type Half Life Washout Time On-Label Uses Off-Label Uses
Yocon Yohimbine  45 minutes 4 hours Erectile Dysfunction  

5.1.2  Treating Sexual Desire Disorders

The condition of low or absent sexual desire has been given many names, such as low libido, or Inadequate Sexual Desire (ISD). The term that will be used here is Hypoactive Sexual Desire (HSD). Whatever the name, it is important to realize that the level of sexual desire varies widely. The definition of healthy sexual desire, and therefore of inadequate sexual desire, depends on the satisfaction of the person or couple involved. An individual's level of desire is only "low" if it makes the individual, or couple, unhappy.
HSD often arises from psychological problems, such as marital problems, past trauma, or other life experiences; however, psychological treatments for HSD are beyond the scope of this book.
A number of medications are useful for treating HSD that arises from physical, rather than psychological, problems, although none of them have been not approved specifically by the Food and Drug Administration (FDA) for this purpose. (All of the medications described below have been officially approved by the FDA for other purposes.) However, physicians frequently use their own judgment and prescribe medications for off-label uses, so there is nothing unusual about the practice.
Antidepressant medications that increase serotonin concentration (serotonergic antidepressants) frequently cause HSD. Some of the medications described below help primarily with HSD that is due to serotonergic antidepressants; some are useful whether or not such antidepressants are the cause; and some are useful only for people who are not taking these antidepressants.  Hormone Therapy

Many endocrine (hormonal) disorders have the potential to cause HSD. If HSD is not an obvious consequence of life circumstances, medication, or illness, then an endocrine disorder is a likely culprit. Thus the first step in the medical treatment of HSD is to see a doctor for a thorough examination, to determine if the problem is hormonal in nature. If at all possible, it is better to see an Endocrinologist than a General Practitioner, as the latter generally lack the knowledge to diagnose the more complex hormonal problems.
Common endocrine problems that can cause HSD include thyroid disorders of various kinds, low testosterone levels, and high prolactin levels. These and other endocrine problems can be treated successfully by a competent Endocrinologist. (However, HSD that arises from serotonergic antidepressants is not treatable by hormone therapy.)
One should look for other medical treatments for HSD only if endocrine problems have been ruled out. The following sections assume either that HSD has no endocrine component, or that any endocrine problems that exist have been treated, but the HSD remains unresolved.  Dopaminergic Medications

The hormone prolactin serves useful purposes in the body, most notably in stimulating milk production in pregnant and nursing women. However, an excess of prolactin can sharply decrease libido in both men and women. Since the rate at which prolactin is produced decreases as dopamine concentration increases, one effective way to treat HSD is by the use of dopaminergic medications. These medications either increase dopamine concentration, or (in the case of dopamine agonists) provide a substitute for dopamine. Dopaminergic medications are perhaps the best approximations to the concept of aphrodisiacs as any prescription medications available today.
The dopaminergic medications described in this section may be useful for HSD problems whether or not the problems are caused by serotonergic antidepressants. They can usually be taken in conjunction with antidepressant medications.
The medication Levodopa, or l-dopa, is not included in the list of useful dopaminergic medications. The omission may seem odd, given that l-dopa is a dopamine precursor, which is converted to dopamine. Like the dopamine agonists and Selegiline, it is used to treat Parkinson's disease. The reason it is not suggested for the treatment of sexual dysfunction is because there has been some speculation that l-dopa may cause degradation of dopamine-emitting neurons over time. Its use in Parkinson's disease may be required, but its use for other purposes is not advised.   Bupropion (Wellbutrin)  
This antidepressant (see Section 2.5.7) provides a modest increase in dopamine concentration. It is the least effective of the dopaminergic augmentations discussed in this section, but because it is a standard antidepressant, it is also the most widely-used, and familiar to physicians.   Dopamine Agonists  
These medications act as substitutes for dopamine, rather than increase its concentration (see Section 2.7). Like Selegiline (Sections 2.4.3 and, they can have a dramatic effect on libido; unlike Selegiline, they may be used freely with SSRIs or other serotonergic medications. Also unlike Selegiline, they do not increase norepinephrine levels, and thus have no effect on energy or concentration.
As noted in Section 2.7, Amantadine is the weakest of the dopamine agonists, while the others may be expected to be of comparable effectiveness. Of the latter, Cabergoline is considered to be the most easily tolerated (least likely to cause unpleasant side effects).   Selegiline  
Selegiline, a selective MAO inhibitor (Section 2.4.3), is another dopaminergic medication. While it has been known since 1965, and long used to treat Parkinson's disease, it has only recently been approved by the Food and Drug Administration (FDA) for the treatment of depression, and only in transdermal form (i.e., supplied by the Emsam skin patch). However, the oral form provides comparable benefits, and is readily available. The two forms should be equally effective in treating HSD.
Selegiline is noteworthy as the only prescription medication that dramatically increases the concentration of dopamine in the brain (aside from l-dopa), without affecting serotonin (except at high doses). As a result, it can have a dramatic effect on libido. It is also a stimulating medication, meaning that it improves energy and concentration, because it also increases the concentration of norepinephrine. Like the dopamine agonists of Sections 2.7 and, Selegiline is about as close to the concept of an aphrodisiac as any prescription medication currently available.
Unfortunately, standard prescribing requirements state that Selegiline cannot be used in conjunction with any other antidepressant (although one could make the argument that this proscription probably should apply, at least at lower doses, only to serotonergic antidepressants). The reason for this prohibition is that it is in the category of MAO inhibitors, and MAO inhibitors are notorious for their drug-interaction problems. On the other hand, while it is certainly true that the more well-known MAOIs (Isocarboxazid, Phenelzine, and Tranylcypromine) must not be taken with, say, an SSRI, as the combination can cause an overdose of serotonin known as Serotonin Syndrome, it is also the case that Selegiline does not affect serotonin levels significantly at low doses (10 mg or less). Thus it seems plausible that one might be able to take Selegiline along with an SSRI. However, this combination is currently forbidden in standard medical practice, and must be regarded as such pending further investigation.  Partial Serotonin Agonists

Buspirone (BuSpar) has been found to be useful for problems of both HSD and Anorgasmia, whether or not the problems are caused by serotonergic antidepressants. It can usually be taken in conjunction with antidepressant medications.
Buspirone acts as an agonist to serotonin 1A receptors, and an antagonist to a norepinephrine receptors. Exactly why Buspirone alleviates sexual dysfunction is not clear, but it has been found to be beneficial.

Main Brand Name Chemical Name Chemical Type Half Life Washout Time On-Label Uses Off-Label Uses
BuSpar Buspirone  24 hours 5 days anxiety Sexual Dysfunction

5.2  Antidepressant-Induced Sexual Dysfunction

As Section 1.4.1 indicated, medications that increase the concentration of serotonin frequently have adverse effects on sexuality. The sexual problems that can occur include loss of libido (Hypoactive Sexual Desire), erectile dysfunction, and anorgasmia. A particular person may experience any or all of these effects, to any degree.
Psychiatrists and pharmaceutical companies were slow to recognize (or admit) that medications used to treat depression could cause sexual problems. As of this writing, the problems are now well known, and are clearly a consequence of the increase in serotonin concentration, which has the following effects:
Unfortunately, there is no consensus on how to alleviate sexual dysfunction induced by psychotropic medications. As of this writing, too little research has been done on treatment strategies for well-tested methods to emerge.
However, the situation is not quite as bleak as it may seem. Although their effectiveness may not always have been confirmed by clinical studies, solutions for overcoming sexual dysfunction do exist. They aren't perfect, and none of them is guaranteed to work for everyone, but there is substantial anecdotal evidence that each works for some people. Many such solutions are described in this chapter.

5.3  Solutions for Dysfunction Caused by Antidepressants

The question naturally arises as to which solution is likely to be the most effective. Unfortunately, the current state of medical science does not provide much guidance in this area. Common sense suggests the following rough guidelines:
Note that it is important to discuss any approach with your doctor before trying it, especially when issues of drug interactions arise. Your doctor should know whether a particular solution is safe for you.
The solutions described in this section are appropriate only for cases where sexual dysfunction is caused by an antidepressant that increases serotonin concentration. Most should be tried only after enough time has passed (four to six weeks) to discover whether the dysfunction is a temporary problem associated with starting the medication, or a permanent side effect of the medication. A particular solution may help with none, some, or all of the types of sexual dysfunction, depending on the individual's response. In addition, the medications described in Section 5.1 may also be used, unless otherwise indicated.
See also www.sexualwholeness.com/isw/resources/7092/boyarsky2000.pdf for a good description of these treatment strategies.

5.3.1  Dose Time Change

Changing the time of day at which the medication is taken may help, if the medication has a short enough half-life. (For example, Fluvoxamine, i.e. Luvox, has a half-life of 16 hours.) Taking the day's dose just after the usual time for sexual activity (for example, at bedtime) guarantees that the amount of the medication in the body, and any consequent sexual impairment, is at its lowest level at that time.
This approach will not work for medications with half-lives that are much longer than the standard daily dosing interval, such as Fluoxetine (Prozac). (On the other hand, Fluoxetine may also be taken on a weekly basis, an approach that might provide a longer window of sexual capability towards the end of each week.)

5.3.2  Drug Holidays

This approach is also most appropriate for medications with shorter half-lives. Omitting the daily dose for one or two days every week may allow for more normal sexual function during those days.
Drug holidays have some drawbacks. First, it increases the likelihood that depression may return during the "holiday" periods. Second, it may interfere with the treatment of depression in general. Third, some medications may produce unpleasant withdrawal effects during this period, which eliminate or outweigh any possible benefits. For these reasons, it is important to work closely with your doctor when attempting this approach.

5.3.3  Dose Reduction

One of the most obvious techniques for improving sexual function is to reduce the dose of the medication that is causing the problem. It may be, for example, that sexual dysfunction becomes a problem at a 30 mg dose, while a 20 mg dose suffices to treat the illness. In this case, reducing the dosage to the minimum required to achieve the benefits may result in escaping the sexual problem.

5.3.4  Medication Change

Another obvious technique for treating sexual dysfunction produced by a medication is to try a different medication. Assuming that the medication is a serotonergic antidepressant, there are a few possible cases, ordered by decreasing likelihood of improvement in sexual function.
  1. Switch to a non-serotonergic antidepressant, such as Bupropion (Section 2.5.7), Selegiline (Section, or Tianeptine (Section 2.5.9). This approach is likely to work very well, as far as sexual function is concerned, but if the particular case of depression requires a serotonergic medication for successful treatment, then this approach is not an option. (Note, however, that Selegiline does increase serotonin concentration when taken at sufficiently high doses, so this is a possible option for people who do require a serotonin boost.)
  2. Switch to, or add, Mirtazapine (Section 2.5.8), Nefazodone (Section 2.5.4), or Trazodone (Section 2.5.4). (These tricyclic antidepressants (and, to a lesser extent, Nortriptyline) blockade the serotonin 5-HT2A receptors specifically. As a result, they provide serotonergic benefits that alleviate depression, but with less impact on sexual function. Since SSRI-induced insomnia is also associated with stimulation of the 5-HT2A receptors, these medications can alleviate the insomnia as well.)
    Drawbacks of Mirtazapine include the possibility of dry mouth, drowsiness, or weight gain. Drawbacks of Nefazodone and Trazodone include the possibility of drowsiness and dizziness.
  3. Switch to a different serotonergic medication, e.g. from one SSRI to another SSRI, to an SNRI, or to a non-selective MAO inhibitor. It may be that a different medicine will provide the antidepressant benefits without the sexual problems.

5.3.5  Temporary Augmentation with a Serotonin Antagonist

A "drug holiday" is one way to take a break from the serotonergic effects that cause sexual dysfunction. Another way is to turn off the serotonergic effects chemically, by blocking the serotonin receptors that cause the dysfunction. Some of the tricyclic antidepressants have this effect (see Section 5.3.4), and can be taken on a daily basis for this purpose.
A different approach to is to take a short-lived medication that blocks serotonin receptors (a serotonin antagonist). Sexual function should improve during the blockade period. As the medication disappears from the body, the serotonergic effects (both good and bad) return. The allergy medication Cyproheptadine (Periactin) may be used for this purpose.7
Cyproheptadine is a combined serotonin and histamine antagonist. It can be effective in alleviating sexual dysfunction, but it has two drawbacks. The first drawback is the usual set of antihistamine side effects, such as drowsiness. The second is that, since it acts to oppose a serotonergic antidepressant, it can suppress any benefits from the antidepressant. Thus undesirable feelings (depression, anxiety, etc.) that have been treated successfully by the antidepressant may also return.
It is important to use a serotonin antagonist only as needed to alleviate sexual dysfunction. Frequent use could render the antidepressant ineffective and negate all of its benefits.

Main Brand Name Chemical Name Chemical Type Half Life Washout Time On-Label Uses Off-Label Uses
Periactin Cyproheptadine  4 hours 1 day Allergies; Headache Sexual Dysfunction (Antidepressant-induced)

5.3.6  Cholinergic Enhancers

A "cholinergic" medication is one that enhances the affects of the neurotransmitter acetylcholine, either by simulating it (as an agonist), or by acting to increase its concentration. Cholinergic medications can reverse problems with muscle weakness (Myasthenia Gravis), control Glaucoma, or treat urinary retention by improving muscular function in the urinary tract.
Neostigmine is a cholinesterase inhibitor that increases acetylcholine concentration by inhibiting the enzyme (acetylcholinesterase) that destroys acetylcholine. It has been used to enhance libido and treat anorgasmia induced by SSRI medications.
Bethanechol has been found useful for treating ED caused by the anti-cholinergic effects of many tricyclic antidepressants.

Main Brand Name Chemical Name Chemical Type Half Life Washout Time On-Label Uses Off-Label Uses
Prostigmin Neostigmine  1 hour 5 hours Myasthenia Gravis Sexual Dysfunction (Antidepressant-induced)
Urecholine Bethanechol  30 minutes 2 hours Urinary Retention Sexual Dysfunction (Antidepressant-induced)

5.3.7  Other Augmentations

The author has heard one anecdotal report that taking the SNRI Reboxetine, along with an SSRI, has alleviated sexual dysfunction due to the latter, although it is not clear why this should be the case.

5.4  Solutions for Problems Caused by Antipsychotics

All antipsychotic medications work by blockading (blocking) the dopamine D2 receptors in the brain, thus reducing the amount of dopamine-related signaling. (See Chapter 4 for details.) The reduction in dopamine activity alleviates psychosis, but can cause numerous difficulties. This section is concerned specifically with antipsychotic-induced sexual dysfunction, and will not address other undesirable side effects of these medications.
Antipsychotic medications are divided into two categories: "typical" and "atypical" antipsychotics. The older, typical antipsychotics blockade D2 receptors throughout the brain. The newer, atypical antipsychotics are more selective, and preferentially blockade D2 receptors in the Mesolimbic Dopamine Pathway, which is the area where excess dopamine activity seems to produce the so-called "positive" psychotic symptoms such as hallucinations. The greater specificity of action of the atypical antipsychotics substantially reduces the undesirable side effects (including sexual dysfunction), compared to the typical antipsychotics, but does not eliminate them.
It appears that sexual dysfunction is a side effect that results from blockading D2 dopamine receptors in the Tuberoinfundibular Dopamine Pathway. Dopamine activity in this pathway controls the rate at which the pituitary gland releases the hormone prolactin. Dopamine blockade in this area causes the pituitary gland to release excess prolactin, which, in sufficiently large amounts, causes hyperprolactinemia. Excess prolactin decreases libido, reducing or eliminating sexual desire. In addition, it can cause reduction in the hormones testosterone and estrogen, negatively affecting libido, erectile function, fertility, bone density in women (osteoporosis), and other aspects of the patient's health.
Treatment of antipsychotic-induced sexual disorder is difficult, as the same neurotransmitter (dopamine) is involved both in libido, and positive psychotic symptoms (such as hallucinations). Simply increasing dopamine activity, in order to alleviate sexual dysfunction, may counteract the benefits of the antipsychotic and trigger psychotic episodes. Thus treatment is largely a balancing act between the needs of the treatment for psychosis on the one hand, and the treatment of suppressed libido on the other. (See www.medsafe.govt.nz/Profs/PUarticles/hyperpro.htm for a good description of the issues involved)
The treatment strategies for antipsychotic-induced sexual dysfunction are essentially a subset of those for antidepressant-induced sexual dysfunction, except that "antidepressant" is replaced by "antipsychotic." The relevant strategies will not be repeated here in detail, but are listed below:
More research is needed to find better ways to treat sexual dysfunction caused by antipsychotic medications.

5.5  Conclusion

The bad news is that medications taken to improve mental health may degrade sexual health. The good news is that, for many people, effective remedies for sexual dysfunction do exist. Much as is the case with antidepressants taken for depression, one may have to try several of the existing remedies for sexual dysfunction in order to find one that works satisfactorily. In this matter, as is so often the case with psychotropic medications, patience is as much a necessity as a virtue.