"We need to be much more cautious about the widespread use of these drugs," says Paul Andrews, an evolutionary biologist at McMaster University and lead author of the article, published in the online journal Frontiers in Psychology.
"It's important because millions of people are prescribed anti-depressants each year, and the conventional wisdom about these drugs is that they're safe and effective."
Andrews and his colleagues examined previous patient studies into the effects of anti-depressants and determined that the benefits of most anti-depressants, even taken at their best, compare poorly to the risks, which include premature death in elderly patients.
Anti-depressants are designed to relieve the symptoms of depression by increasing the levels of serotonin in the brain, where it regulates mood. The vast majority of serotonin that the body produces, though, is used for other purposes, including digestion, forming blood clots at wound sites, reproduction and development.
What the researchers found is that anti-depressants have negative health effects on all processes normally regulated by serotonin.
The findings include these elevated risks:
- developmental problems in infants
- problems with sexual stimulation and function and sperm development in adults
- digestive problems such as diarrhea, constipation, indigestion and bloating
- abnormal bleeding and stroke in the elderly
"Serotonin is an ancient chemical. It's intimately regulating many different processes, and when you interfere with these things you can expect, from an evolutionary perspective, that it's going to cause some harm," Andrews says.
Millions of people are prescribed anti-depressants every year, and while the conclusions may seem surprising, Andrews says much of the evidence has long been apparent and available.
"The thing that's been missing in the debates about anti-depressants is an overall assessment of all these negative effects relative to their potential beneficial effects," he says. "Most of this evidence has been out there for years and nobody has been looking at this basic issue."
In previous research, Andrews and his colleagues had questioned the effectiveness of anti-depressants even for their prescribed function, finding that patients were more likely to suffer relapse after going off their medications as their brains worked to re-establish equilibrium.
With even the intended function of anti-depressants in question, Andrews says it is important to look critically at their continuing use.
"It could change the way we think about such major pharmaceutical drugs," he says. "You've got a minimal benefit, a laundry list of negative effects - some small, some rare and some not so rare. The issue is: does the list of negative effects outweigh the minimal benefit?"
A video of Paul Andrews discussing the research: