False Alarm: Study Doesn't Link Prozac to Cancer

From the WebMD Archives

March 28, 2002 -- A British study widely reported to link Prozac to cancer does no such thing.

The study appears in the April 1 issue of the journal Blood. News headlines immediately heralded the findings as evidence that the antidepressants Prozac, Paxil, Zoloft, and Celexa can cause cancer.

This came as a complete surprise to study leader John Gordon, PhD, immunologist at England's University of Birmingham.

"There is nothing here to link antidepressants to cancer," Gordon tells WebMD.

Gordon and co-workers weren't even studying antidepressants -- they were just using them as a tool. Their study showed that serotonin -- a brain chemical also found throughout the body -- helps fight a kind of blood tumor called Burkitt's lymphoma. Serotonin, they found, triggers the self-destruct mechanism inside tumor cells.

Prozac, Paxil, Zoloft, and Celexa belong to a class of antidepressants called selective serotonin reuptake inhibitors, or SSRIs. They increase the amount of serotonin acting on the brain. They don't increase serotonin production. Instead, they block a carrier molecule that normally whisks the serotonin away.

Gordon's team guessed that this same kind of carrier molecule sits outside cancer cells. Their theory was that it whisks serotonin into the cell, beginning the process of tumor destruction. But how were they to prove it? Their answer was to expose the cells to SSRI antidepressants. Sure enough, the drugs blocked the carrier molecule and kept the serotonin out of the cell. This kept the cancer cells alive -- in the test tube.

Does this mean that a person who takes SSRIs loses the ability to fight cancer? No, Gordon says.

"It is very different when you have cells all by themselves in the test tube and you add known components," he insists. "We have no idea whatsoever what the interactions would be in the body."

Eli Lilly and Company, the maker of Prozac, is a WebMD sponsor.

"There is no medical or scientific evidence that shows a connection between Prozac and cancer," says Lilly spokeswoman Anne Griffin. "We have 20 years of experience with over 40 million patients who have taken Prozac. Never has such a link been found."

There definitely is no proof that antidepressants cause cancer. This doesn't mean that there might not be a link, says cancer researcher Lorne J. Brandes, MD. Brandes is professor of medicine and pharmacology at the University of Manitoba in Winnipeg.

Brandes says he conducted studies in which antidepressants, including Prozac, sped the growth of malignant tumors in mice. He's recently reviewed the medical literature on the topic. Several studies link antidepressants to breast and ovarian cancer; other studies show no link.

"We all know depression is a very serious disease and antidepressants help a lot of people," Brandes tells WebMD. "The question is whether any of these drugs have an unintentional effect on cancer. There are all these things that keep coming up and popping up in the medical journals. I think there is something to this whole story."

Brandes says he finds it ironic that it is the Gordon study, which had nothing to do with actual use of antidepressants, that has created such a stir.

Gordon, too, says he finds it ironic -- especially since he sees his work as an important step toward new treatments for cancer.

"I've been in this game 25 years, and we feel this is the most exciting finding we have had in terms of hopefully developing a cancer therapy somewhere down the line," he says.

All of the experts who spoke to WebMD urge people taking antidepressants to keep taking their medications. All agree that while cancer risk remains theoretical, the dangers of depression are very real. They say that people who are worried about possible side effects from long-term use of these medicines should discuss the issue with their doctors.