Viagra works by increasing blood flow to the genitals. In contrast, flibanserin's target lies in the brain, as Clare Wilson reports for New Scientist. In animal studies, it increases levels of two neurotransmitter molecules in the brain: dopamine, which controls the brain's reward pathways, and norepinephrine, the hormone that helps the brain focus in stressful situations. At the same time, the drug causes a decrease in levels of serotonin, the so-called "happiness" hormone. Researchers aren't entirely sure why this combination of chemical levels results in an increased libido, but studies suggest that it does.
In fact, the German drug firm Boehringer Ingelheim initially developed the compound as an anti-depressant, but it flopped in that department. When women reported feeling an increase in libido, though, the company refocused their efforts. But, they had trouble showing that the drug had a significant effect, as Amanda Holpuch explains for The Guardian. In 2010, the FDA rejected Boehringer Ingelheim's proposal to market flibanserin in the United States, so they dropped the drug. Sprout Pharmaceuticals picked it up and again submitted it for approval in 2013. The FDA nixed it, again.
In clinical trials, women taking the drug reported having one more "satisfying sexual encounter" per month than normal. Given that the drug also comes with side effects like sudden drops in blood pressure, sleepiness and fainting spells, it's unclear whether the benefits outweigh risks, Wilson writes. That's what has kept flibanserin off the market in the past. With the support of women’s groups and politicians, this time around Sprout hopes to change that by recasting the drug as the feminist counterpart to the infamous little blue pill. (Not all women's health groups are on board, though.)
Not only do the two drugs work on entirely different mechanisms, they also treat totally different sexual issues. Viagra and similar drugs for men treat impotency, often caused by a drop in blood flow to the genital area. It's an easy enough thing to fix. Thus, the drug corrects the issue by simply increasing circulation to the region. Viagra does nothing to increase desire in the brain.
