A new study showed that popular antidepressants have little impact on most patients, if none.

Researchers from the UK, U.S. and Canada analyzed results of 47 clinical trials (which were submitted to the U.S. Food and Drug Administration before approval)involving Fluoxetine (better known by the brand name Prozac), venlafaxine (Effexor), nefazodone (Serzone) and Paroxetine (Paxil or Seroxat), all members of a class of drugs known as selective serotonin reuptake inhibitors (SSRIs).

The study says antidepressants are barely more effective than a placebo in mild cases of depression. Only patients diagnosed “at the upper end of the very severely depressed category” know a slight improvement in their condition.

“Although patients get better when they take antidepressants, they also get better when they take a placebo, and the difference in improvement is not great. This means that depressed people can improve without chemical treatments,” Irving Kirsch of the University of Hull, in northern England, lead author of the study said in a statement, according to the Associated Press.

Moreover, Prof. Kirsch stated that these antidepressants were approved by the FDA, but only showed just enough effect on patients to get the green light for sale.

Based on the findings, the researchers concluded that antidepressants should only be prescribed to the most severe depression cases. Prof. Kirsch suggested that people with mild depression should first try alternative treatments, which include physical exercises as well as counseling with a psychiatrist or something of that nature.

“Most patients can benefits as much from other treatment, such as physical exercise and psychotherapy, as they can from medication. Antidepressants should be reserved for patients at the very extreme levels of depression.”

Dr. Nada Stotland, president-elect of the American Psychiatric Association was not surprised by the findings.

“Medication helps some, but not all, people with depression. For people with mild to moderate depression, psychotherapy can work as well as medication. Studies have shown that between 70 and 80 percent of people can and do get better with a combination of treatment approaches, which will often include individual therapy, family therapy, and/or medication,” Dr. Stotland said, quoted by the Washington Post.

Drug makers rushed to contain damage to their future sales. Eli Lilly, GlaxoSmithKline and others involved in the antidepressants market rushed out statements upholding the effectiveness of their SSRIs.

The study titled “Initial Severity and Antidepressant Benefits: A Meta-Analysis of Data Submitted to the Food and Drug Administration” was published in the online journal Public Library of Science.