Drugs such as Prozac, Zoloft, Celexa and Paxil may slightly raise the risk of brain hemorrhage, Canadian researchers reported in the journal Neurology. The authors emphasized that even though the likelihood of bleeding in the brain is increased slightly, it is still a very small risk.

They were talking specifically about SSRIs (selective serotonin reuptake inhibitors); very widely used drugs. Although for the individual the risk remains small, the difference when calculated on a national scale could involve a large number of people.

Stomach bleeding has been associated with the use of SSRIs. Studies on whether they are linked to brain hemorrhages have produced conflicting results.

Daniel Hackam, from the Western University in London, Ontario, Canada, and colleagues gathered data on the results of 16 studies with information on half a million people; some of them were taking SSRIs; they were compared to others of the same age who were not.

They found that overall, SSRI antidepressant users had a 40% to 50% higher chance of suffering from bleeding either around or in the brain.

Although such an increase may sound large, the authors insist the risk still remains “extremely low”. Somebody on an SSRI for over one year has a 1 in 10,000 chance of developing a brain hemorrhage.

The researchers said that it is not possible to definitely blame the SSRIs for the bleeding in the brain risk. They did not check to see whether there is a higher incidence of diseases or conditions linked to brain hemorrhages among people on antidepressants.

The authors said they tried to factor in variables that might confound the results of the various studies, but were unable to. Some of the studies simply did not contain the key data they required, including smoking status, how much alcohol patients consumed, their bodyweights, and whether they had chronic diseases, such as diabetes type 2.

It was impossible to infer cause and effect from the 16 studies they examined.

One finding which appeared on most of the studies was a higher risk of brain hemorrhage during the first few months after patients started taking SSRIs. If the risk dropped after the first few months, it makes it less likely, but not definite, that other factors were causing the brain bleeding.

We know that SSRIs make it harder for platelets to form clots. During the initial weeks after starting on the antidepressants, there may be a significant reduction in a person’s platelet functions.

The authors urged patients not to worry. They stressed that overall, these types of antidepressants are relatively safe.

They suggest that doctors should be careful when deciding what to prescribe depressive patients who are already at high risk of brain hemorrhage. Apart from those with a medical history of stroke, individuals on medications to reduce blood clotting may also have a high risk.

In an Abstract in the same journal, the authors wrote: