A large scale study has found that all but two of the newer anti-depressant drugs cause significant sexual dysfunction (SD). The study included 6,297 patients reporting data to their primary care physicians at 1,101 clinics across the United States. The data was presented at the American Psychiatric Association annual meeting on Tuesday May 8 2001.

The study found that patients taking either bupropion SR (Wellbutrin) or nefazodone(Serzone) had a lower prevalence of SD than patients taking fluoxetine (Prozac), paroxetine (Paxil), sertraline (Zoloft) or venlafaxine XR (Effexor). (2005 edit - Nefazodone (Serzone) was removed from the U.S. market in 2004, leaving bupropion as the only currently available newer antidepressant without sexual side effects).

The results get complicated at this point. According to the study patients taking bupropion SR had a significantly lower prevalence of sexual dysfunction than patients taking citalopram (Celexa) or mirtazapine (Remeron).

Patients taking a slightly different medication, bupropion IR, also had a significantly lower prevalence of SD than patients who were taking paroxetine, sertraline or venlafaxine XR. Patients taking fluoxetine (Prozac) had a lower prevalence of SD than patients taking paroxetine.

Wellbutrin and Serzone appear to affect the brain in a different way from the other drugs in the study because they bind to cells at a different receptor site.

Participants in this study were chosen partly because they stated that they were willing to talk about their sex lives. Physicians had estimated that about 20 percent of patients taking antidepressants would report SD. Fully 37 percent of patients were actually found to have sexual dysfunction.

Risk factors for SD included increasing age, higher antidepressant dose, being married, education level less than a college degree, employment status other than full-time, having another illness associated with SD, or taking more medications that just the antidepressant. Patients who did not have a history of sexual enjoyment, had low interest in sexual functioning, or had a history of SD with previous antidepressant therapy were also at greater risk for SD. Smokers who smoked six to 20 cigarettes per day were also at greater risk.

Reference: Clayton & Pradko, Poster presented at the Annual Meeting of the American Psychiatric Association, May 2001.

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From Leonard Holmes, former About.com Guide