Common anti-depressants seem to be doing patients more harm than good, says a new study. "We need to be much more cautious about the widespread use of these drugs," says Paul Andrews, evolutionary biologist at McMaster University, Canada, who led the study. "Millions of people are prescribed anti-depressants every year, and the conventional wisdom about these drugs is that they are safe and effective," said Andrews, the journal Frontiers in Psychology reports. Andrews and his colleagues examined previous studies about the effects of anti-depressants and determined that even taken at their best, most anti-depressants compare poorly to the risks, which include premature death in elderly patients, according to a McMaster statement. Anti-depressants are designed to ease 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 clot at wound sites, reproduction and development. Researchers found that anti-depressants have negative effects on all processes normally regulated by serotonin in the body. The negative health impacts include elevated risks, such as, developmental problems in infants, problems with sexual stimulation, sperm development, digestive problems such as diarrhoea, constipation, indigestion, bloating, abnormal bleeding and heart ailments in the elderly. The researchers reviewed three recent studies showing that elderly anti-depressant users are more likely to die than non-users, even after taking other important variables into account. The higher death rates indicate that the overall effect of these drugs on the body is more harmful than beneficial. "Serotonin intimately regulates many different processes in the body, and when you interfere with it you can expect, from an evolutionary perspective, that it`s going to cause some harm," says Andrews.