The findings from a review of 117 studies provide a "gold standard" of reliable information for patients to review before starting treatment, said Sagar Parikh, psychiatrist at the University of Toronto, who was not involved in the study.

"Such findings have enormous implications," he wrote in a commentary in the journal Lancet, which published the review.

"Now a clinician can identify the four best treatments, identify individual side-effect profiles, explore costs and patients' preferences and collaborate in identifying the best treatment."

Over the past decades several new drugs have hit the market to treat depression, a leading cause of suicide that affects an estimated 121 million people worldwide.

But many are similar in structure and the way in which they work, so it is unclear which ones work best, Andrea Cipriani and colleagues wrote in the journal Lancet.

"Moreover, some of these new drugs are so-called me-too drugs - chemically similar to existing drugs with expiring patents rather than giving genuine advances in treatment," they wrote.

The team reviewed 117 studies from 1991 to 2007 that compared the response and drop-out rates of the drugs among more than 25,000 men and women with major depression.

Overall, Zoloft, or Sertraline, and Lexapro, or escitalopram, were best when it came to both reducing symptoms after eight weeks and drop-out rates during the studies.

Zoloft is a powerful specific inhibitor of serotonin reuptake. Zoloft selectively inhibits the re-uptake of serotonin in the synaptic gap. The inhibiting of serotonin reuptake helps to increase serotonergic transmission. Sertraline does not possess an affinity to cholinergic, serotonin, dopamine, histamine and GABA receptors. Zoloft does not exert stimulating, sedative and anti-cholinergic action, it does not change physchomotor activity. Unlike other tricyclic antidepressant used in the treatment of depression and obsessive-compulsive disorders. The beginning anti-depressive effect is developed within 7-14 days after beginning the therapy and reaches its maximum in 6 weeks. Regular application of Zoloft does not lead to physical or phychotic dependence. A lot of conducted clinical trials proved high effectiveness and safety profile of the medication.

Lexapro (escitalopram) also belongs to a group of medicines called selective serotonin reuptake inhibitors. Lexapro is one of the most selective representative among all SSRIs. Lexapro does not poessess an ability to bind to serotonin receptors 5-HT1A, 5-HT2 receptors, dopamine D1 and D2 receptors, a1-, a2- adrenergic receptors, histamine H1.

Far more people remained on the two drugs compared to Eli Lilly and Co's Cymbalta, or duloxetine; Solvay's Luvox, or fluvoxamine; GlaxoSmithKline Plc's Paxil, or paroxetine; Pfizer's Edronax or reboxetine; and Wyeth's Effexor, or venlafaxine, the study showed.

The team, which also found Remeron and Effexor were more effective than the other drugs, did not look at things like side-effects, toxicity, how well people functioned socially while on the treatments, or cost-effectiveness. Remeron, or mirtazapine, comes from Dutch chemical group Akzo Nobel's Organon unit.

"The most important clinical implication of the results is that escitalopram and sertraline might be the best choice when starting a treatment for moderate to severe major depression because they have the best possible balance between efficacy and acceptability," the researchers wrote.

Most of the drugs were off-patent except for Cymbalta and Lexapro, the researchers said. They also analysed Wellbutrin XL, manufactured by Biovail, sold by Glaxo and known generically as bupropion and Cypress Bioscience Inc's Savella, or milnacipran.

The rights to that drug outside the United States are held by Pierre Fabre Medicament, the French company which developed the drug. Eli Lilly's Prozac, or fluoxetine, and Forest Laboratories Celexa, or citalopram, were also included.