What Happens If a Woman Takes Viagra?

Sildenafil was created by two Pfizer scientists in 1989. The drug works on the phosphodiesterase-5 (PDE5) enzyme, found primarily in the lungs, to relax the blood vessels and lessen the workload of the heart. For this reason, researchers believed it could be a potential treatment for high blood pressure and angina, a type of chest pain associated with coronary heart disease.

Sildenafil went into human clinical trials in the early 1990s but didn't perform well as a heart treatment. However, researchers found that it did perform quite well in the bedroom, at least according to male participants enrolled in the studies. Men taking the drug reported it gave them the unusual side effect of increased erections several days after taking the initial dose. The more clinical trials Pfizer conducted, the more reports of erection side effects it documented.

"Coincidentally, around the same time, other studies were revealing more information about the biochemical pathway involved in the erection process," executive director of discovery research at Pfizer Global Research & Development's Sandwich Laboratories Ian Osterloh wrote in an April 2015 issue of Cosmos magazine. "This helped us understand how the drug might amplify the effects of sexual stimulation in opening up the blood vessels in the penis."

So how exactly is Viagra triggered when a man is sexually stimulated? Here's what happens:

When a man is aroused, his body releases nitric oxide into the erectile tissue of his penis, which stimulates an enzyme that produces cyclic guanosine monophosphate (cGMP). This causes the smooth muscle cells to relax and the arteries in the penis to dilate, which increases the blood flow to the penis and causes the erectile tissue to also fill with blood. The combination results in an erection. Viagra works by maintaining the level of cGMP in the smooth muscle cells, which are only present in the first place when a man is turned on.

With the chances of sildenafil becoming a heart treatment fading fast, Pfizer decided to run pilot studies in male patients who were impotent. The positive results got a rise out of researchers and study participants alike, and Pfizer quickly sought regulatory approval from the U.S. Food and Drug Administration (FDA).

In March 1998, the FDA approved sildenafil as a treatment for erectile dysfunction — the new clinical name for impotence. Pfizer marketed it under the brand name Viagra. This was such a big deal sales of "the "little blue pill" shot through the roof. In the first two months, Pfizer made more than $182 million in revenue, almost twice the revenue of the five leading drug launches of 1997 combined. Ten years later, Viagra was pulling in upward of $2 billion in annual sales.

Remember how Viagra works? It dilates blood vessels and increases blood flow. Sure, it engorges the penis and, researchers presumed, may also increase blood flow to the female genitalia and stimulate sexual arousal.

This hypothesis was put to the test in 2003 by researchers from the University of California, Los Angeles, urology department. They studied the effects of sildenafil on postmenopausal women experiencing a lack of sexual interest and willingness to be sexual, a condition known as female sexual arousal disorder (FSAD), which falls under the umbrella term "female sexual dysfunction," or FSD.

Interestingly enough, researchers found that Viagra helped women in a couple of ways. For instance, the women reported increased genital sensation and increased satisfaction during intercourse and stimulation. However, the women also reported some mild side effects, including headache, flushing, rhinitis and nausea.

Since the 2003 study, however, few other studies have been designed to examine the effects of women taking Viagra. The research shows conflicting results but is nowhere near as effective for improving sex drive in women as it is for improving erectile dysfunction. As such, the FDA has not approved Viagra for women.

As we mentioned, women given Viagra during clinical trials reported some of the same mild side effects as men. But Viagra is also associated with more serious side effects, which can also affect women. These include low blood pressure, allergic reaction, sudden vision loss, sudden hearing loss or ringing in the ears, and dizziness, as well as cardiovascular problems such as chest pain, heart attack, heart failure and stroke.

In fact, in 2000, research was presented at the 49th Annual Scientific Session of the American College of Cardiology that suggested 522 patients died while taking the drug during its first year on the market. Viagra can also interact adversely with several medications. For example, Viagra can cause dangerously low blood pressure if taken with nitrates or alpha blockers.

There are a few drugs out there approved by the FDA to treat low libido in women that have been wrongly labeled "female Viagra." That's because Viagra is prescribed to treat erectile dysfunction, a physical condition, while these other drug treatments seek to boost sexual interest and improve low sex drive in women. Sex drive is multi-faceted, encompassing both emotional and mental health — Viagra doesn't address physical arousal.

The closest thing to Viagra for women is flibanserin, a drug from a class of medications called serotonin receptor 1A agonists/serotonin receptor 2A antagonists. Flibanserin doesn't dilate blood vessels like Viagra. Instead, it's thought to lower serotonin in the brain (serotonin in the brain is believed to inhibit sexual function) and increase norepinephrine and dopamine neurotransmitters (which may also be relevant).

Flibanserin was approved by the FDA in August 2015 for premenopausal women diagnosed with hypoactive sexual desire disorder (HSDD) not caused by a medical condition, a mental disorder, relationship problems, or by using drugs or other medications. It is marketed by Sprout Pharmaceuticals under the brand-name Addyi. Placebo-controlled clinical trials showed that 46 to 60 percent of women with hypoactive sexual desire disorder reported clear benefit from flibanserin.

Unlike Viagra, which was approved for marketing just two years after it was patented, the FDA rejected Addyi twice — in 2010 and again in 2013 — for marginal effectiveness and concerns of side effects such as somnolence (state of drowsiness or strong desire to sleep), as well as hypotension and syncope (fainting), which could worsen if taken when drinking alcohol. The FDA also questioned study participants' ability to drive the day after they took the drug. Resulting studies detected no driving impairment.

When Addyi applied for FDA approval for a third time in 2015, the clinical trials data presented included the results from more than 11,000 patients — one of the largest data sets ever presented to the FDA for a drug approval. The FDA did approve the drug but with a caveat — a black boxed warning for severely low blood pressure that is exacerbated when combined with drinking alcohol. Black box warnings, also called boxed warnings, are the highest safety-related warning medications can have assigned by the FDA.

If you thought the approval processes for Viagra versus Addyi were a bit unfair, you're not alone. The first two FDA rejections of Addyi were met with claims of gender bias for persistently ignoring female sexual health and sexual activity, which the agency vehemently denied.

But consider the evidence: The FDA fast-tracked the approval of Viagra for male erectile dysfunction within six months with fewer than 2,000 study participants. It took more than five years, additional studies, and more than 11,000 study participants (and three tries) for Addyi to finally be an FDA approved treatment. Even then, the drug's approval was marked by a black box warning.