While antidepressants are usually prescribed to help people overcome depression, a new study suggests that the drugs may in fact be making some people more depressed and causing digestive problems.
This alarming suggestion revolves around the very chemical that is targeted by antidepressants - serotonin.
Drugs like Prozac were hailed in the early Nineties as wonder pills that would expel depressive blues for good.
But in the past five years, growing scientific evidence has shown these drugs work for only a minority of people.
Drugs such as Prozac are called selective serotonin reuptake inhibitors (or SSRIs).
Their objective is to boost the level of this 'feel-good' chemical in the brain.
And now a controversial research points out that serotonin is like a chemical Swiss Army knife, performing a very wide range of jobs in the brain and body.
And when we start deliberately altering serotonin levels, it may lead to a wide range of unwanted effects.
These can comprise digestive problems, sexual difficulties and even strokes and premature deaths in older people, according to the study's lead researcher Paul Andrews.
"We need to be much more cautious about the widespread use of these drugs," the Daily Mail quoted Andrews, an assistant professor of evolutionary psychology at McMaster University in Ontario, Canada. As saying.
Earlier research has suggested that the drugs provide little benefit for most people with mild and moderate depression, and actively help only some of the most severely depressed.
Eminent psychologist Irving Kirsch has found that for many patients, SSRIs are no more effective than a placebo pill.
Two years ago, the Canadian Medical Association Journal reported a 68 per cent increase in risk of miscarriage in women on antidepressants.
And research in 2009 on Danish children found a small, but noteworthy, increase in the risk of heart defects among babies whose mothers had used SSRIs in early pregnancy.
There is also increasing evidence that long-term use in adults is associated with bleeding in the gut and increased risk of stroke.
The key to understanding these side-effects is serotonin, insisted Andrews.
Serotonin is also the reason why patients can frequently end up feeling still more depressed after they have finished a course of SSRI drugs.
He has asserted that SSRI antidepressants interfere with the brain, leaving the patient vulnerable to a 'rebound' depression of even greater intensity than before.
"After prolonged use [when a patient stops taking SSRIs], the brain compensates by lowering its levels of serotonin production," he said, adding that it also changes the way receptors in the brain respond to serotonin, making the brain less sensitive to the chemical.
These changes are considered to be temporary, but studies indicate that the effects may hang on for up to two years.
Relapsing is not exclusive to SSRI drugs and can be seen in all the classes of antidepressant medications - but Andrews believes that the risk is especially strong with SSRI drugs.
Moreover, he cautioned that antidepressants can disrupt all the physical processes that are normally regulated by serotonin, adding that animal studies show only about 5 percent of the body's serotonin lives in the brain. Most is housed in the gut.
It is used, among other things, to control digestion, form blood clots at wound sites, and regulate reproduction and growth.
So a drug that interferes with serotonin may cause developmental problems in infants, problems with sexual stimulation and sperm development in adults, digestive problems such as constipation, diarrhoea, indigestion and bloating, and abnormal bleeding and stroke in the elderly.
The drugs may also raise the risk of dementia.
Most alarmingly of all, Andrews' reviewed features three recent studies which, he said, show that elderly antidepressant users are more vulnerable to die prematurely than non-users, even after taking other important variables into account.
Stafford Lightman, professor of medicine at the University of Bristol, and a leading UK expert in brain chemicals and hormones, said that Andrews' review highlights some important problems, yet it should also be taken with a pinch of salt.
The study has been published in the journal Frontiers In Evolutionary Psychology.