Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressants that includes Prozac and Zoloft. As the name says, SSRIs stop nerves from taking up serotonin. But they could also stop blood platelets from taking up serotonin, which they need to form blood clots. Researchers in the Netherlands looked at whether these antidepressants might cause abnormal bleeding.

What the researchers wanted to know: Do some SSRIs increase the risk of abnormal bleeding more than others?

What they did: The researchers used a big database with prescription information on 850,000 people in the Netherlands. They picked out all the patients who'd gotten a prescription for an antidepressant for the first time between 1992 and 2000 and looked for people who were admitted to the hospital for a bleeding problem. For each person with bleeding, they picked at random five people who were the same sex, about the same age, and had started antidepressants at the same time. Each antidepressant was classified according to how strongly it inhibited the uptake of serotonin—high (including Prozac, Zoloft, and Paxil), intermediate (including Effexor), or low (including Wellbutrin and Manerix).

What they found: Of nearly 65,000 people studied, 196 were hospitalized for abnormal bleeding, most commonly bleeding of the uterus. People on drugs that more highly inhibited serotonin uptake had a higher risk of abnormal bleeding, according to their analysis. Patients on a high-level inhibitor had a 2.6 higher risk than people on a low-level inhibitor.

What the study means to you: Since bleeding seems to be more likely with stronger-inhibiting drugs, it seems likely that SSRIs do increase the risk of bleeding.

Caveats: Since they used only hospitalization records, they couldn't tell if patients had abnormal bleeding that wasn't bad enough for hospitalization or if any patients bled to death before getting to the hospital. So the risk might actually be higher.

Find out more: Information on medications from the National Institute of Mental Health

Read the article: Meijer, W.E.E. et al. "Association of Risk of Abnormal Bleeding With Degree of Serotonin Reputake Inhibition by Antidepressants." Archives of Internal Medicine. Nov. 22, 2004, Vol. 164, pp. 2367–2370.

Abstract online: http://archinte.ama-assn.org