And dopamine, the "wanting" chemical, is what makes us yearn for a piece of chocolate or a promotion at work, and, as Fisher learned in her study (published in 2005), which examined brain scans of 30 people in love, it's also the driving force behind budding desire—the stage when you're anxiously awaiting a call or an email from someone you can't stop thinking about. "When you take SSRIs and drive up serotonin, it stands to reason that you not only suppress dopamine but also romantic love," she says.

LIBIDO BUSTERS
And then there's the randier half of the equation: Some studies show that as many as 70 percent of people taking antidepressants have some sexual dysfunction, according to Anita Clayton, a psychiatrist with the University of Virginia Health System and a leading researcher on these drugs’ sexual side effects. A study she led last year found that women on SSRIs are most likely to experience arousal problems—they can’t get in the mood for sex, either mentally or through vaginal lubrication, and she adds, "they may also have trouble achieving orgasm."

The reasons are twofold: SSRIs lower the levels of testosterone and dopamine in the body, and can also alter vaginal sensation, leaving users without much feeling—or so sensitive that sex is painful. The side effects may go away in time. Often doctors add a new drug to the mix to alleviate them, switch up medications, or, less frequently, recommend a short "vacation." But patients are often reluctant to mess with a formula that’s working—despite the drawbacks.

"I'm totally disinterested in sex," says Daniela Vellotti, 33, of Alpharetta, Georgia, who used to enjoy occasional twice-a-day romps with her long-term boyfriend before going on Zoloft in May. "I've only been able to orgasm twice since going on the drugs, and it wasn't even that good."

The bigger problem, says Fisher, is that unfulfilling sex is more than just a relationship inconvenience—science shows couples need to orgasm to stay in love. Sexual stimulation drives up dopamine, helping fan the fires of romantic love, and orgasm brings a flood of oxytocin, the brain chemical associated with attachment. The bottom line: "Sex drive, romantic love, and attachment are connected," says Fisher, who passionately believes that antidepressants are capable of tampering with that delicate love triangle.

THE NAYSAYERS
Not everyone is convinced. "Our capacity to love is very strong," says Clayton, author of Satisfaction: Women, Sex and the Quest for Intimacy. "I just haven't seen people on SSRIs not be able to fall in love, and there's no good systematic data to suggest that." The very nature of depression places stress on relationships, she says. The last thing a depressed woman is thinking about is falling in love or having sex: "They're focused on their own suffering." By and large, the drug companies also dispute the claims.