What's up with headlines calling Vyleesi a "female Viagra"? Yes, both medications begin with the letter "V" and are designed to address sex-related health issues. But there are real hard differences between these two medications.
The U.S. Food and Drug Administration (FDA) recently approved Vyleesi, generically known as bremelanotide, to "treat acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women." It is important to note that HSDD is not the "female version" of erectile dysfunction or ED. Here's how the FDA defined HSDD in their announcement:
HSDD is characterized by low sexual desire that causes marked distress or interpersonal difficulty and is not due to a co-existing medical or psychiatric condition, problems within the relationship or the effects of a medication or other drug substance. Acquired HSDD develops in a patient who previously experienced no problems with sexual desire. Generalized HSDD refers to HSDD that occurs regardless of the type of sexual activity, situation or partner.
Consider the key aspects of HSDD. It is low sexual desire. The person affected is not OK with and in fact greatly affected by the situation. There isn't an obvious cause, and the issue is persistent across partners, practices, and situations. Therefore, if someone is not interested in just you specifically, you can't blame it on HSDD.
Low sexual desire is a very, very, very complex issue, and scientists haven't even figured out all the pathways that lead to sexual desire. That's in part because sexual desire involves the big brain that sits in one's head and not just the little brain that sits much lower. And the big brain is really complex.
Just take a look at a review article published in the Mayo Clinic Proceedings and authored by the International Society for the Study of Women's Sexual Health (ISSWSH) Expert Consensus Panel. The panel outlined the many different parts of the brain, the neurotransmitters, and the hormones that seem to be involved with sexual excitation. Reading through the article, you'll quickly realize that there are many more questions remaining about HSDD than answers.
Vyleesi is supposed to work by activating melanocortin receptors, which seem to be involved in many different brain functions including regulation of mood and thinking. However, the FDA announcement admits that "the mechanism by which [bremelanotide] improves sexual desire and related distress is unknown." That's quite a bit different from Viagra, where the mechanism is much clearer. But more about that later.
Having HSDD is analogous to saying that your car doesn't even start and you are not sure why or even how the car is supposed to run. Of course, one's brain and body are a lot more complex than a car. In fact, HSDD may actually be a collection of many different causes and issues lumped together simply because they seem to have the similar end result: lack of sexual desire. Any suggestion that there can be a single treatment for all types of HSDD greatly oversimplifies and overlooks the heterogeneity of HSDD.
By contrast, ED alone is a much more straightforward mechanical issue. Having ED doesn't necessarily mean a lack of interest in sex. With ED itself, the motor can be running but you just may not be able get the car out of park, so to speak. ED medications like Viagra, or sildenafil as it's known generically, work by dilating the blood vessels that provide blood flow to the penis. Blood flow is what leads to an erection and not "muscles flexing." So if you are doing some type of weird weight training program to help that part of the body, stop it.
Moreover, you can kind of easily see whether Viagra is working or not. If you don't know what this means, it is just a matter of standing up to see. In fact, even if you have low sexual desire or excitement, ED medications like Viagra can still produce their intended results.
Compare this with how Vyleesi has been evaluated: having study participants answer questionnaires. Answers to the questionnaires then yielded a "sexual desire score" on a scale of 1.2 to 6.0 with a higher score meaning greater desire and a "distress score" on a scale of 0 to 4.0 with a higher score meaning more distress. As you can imagine, such questionnaires and scores are much more subjective than watching a body part change.
In clinical trials, about 25% of study participants who had used Vyleesi for 24 weeks to treat their HSDD experienced increases by at least 1.2 in the "sexual desire score" compared to about 17% of participants who had taken placebo. At the same time, about 35% of those who had taken Vyleesi registered decreases by least 1.0 on their "distress scores" compared to about 31% of those who had taken placebo. These are significant but by no means overwhelming findings.
Another difference between Vylessi, which will be marketed by AMAG Pharmaceuticals, and Viagra is their routes of administration. Viagra goes into your mouth, or at least you it should, whereas Vyleesi gets injected under the skin of your abdomen or thigh at least 45 minutes prior to sex. Taking a pill by mouth is a whole lot simpler than using a needle to inject a medication.
Something else to note. About 40% of the clinical trial participants experienced nausea after Vyleesi injections with 13% having nausea bad enough to necessitate anti-nausea medications. The other side effect of note was gum and skin darkening, particularly in the face and the breasts, which was experienced by about 1% of patients who received Vyleesi in clinical trials.
It remains to be seen how many women who are suffering from HSDD will be willing to try Vylessi and how effective the medication will be in helping them. HSDD is certainly not a rare condition, affecting approximately 10% of adult women, and by definition is something that causes significant distress. Nevertheless, HSDD remains an understudied issue like many women's health issues. The lack of available and effective options led to the FDA's approval of Sprout Pharmaceuticals’ Addyi in 2015, despite controversy over its effectiveness and safety. Addvi is a pill that to be taken once a day with an important warning: it shouldn't be taken with alcohol.
There may be marketing motivations to call Vylessi a "female Viagra." After all, Viagra was a blockbuster medication in so many ways, as I have described previously for Forbes. In the first quarter after its April 1998 launch, Viagra rapidly grew in popularity, topping $400 million in sales. Eventually, annual revenues for the medication rose past $1.8 billion. So if the adoption of Vylessi approaches that of Viagra in any way, it would be boon for AMAG Pharmaceuticals. But don't hold your breath. The commercial success of Viagra would be a hard act to follow for any medication. Plus, HSDD is just very different from ED.
