The Studies conflict as Zoloft, Lexapro and other drugs are tested for effectiveness and side effects and the study says Zoloft and Lexapro are not the best.

The study, published online last month in the medical journal Lancet, compared 12 newer generation antidepressant drugs using data from 117 published clinical studies with nearly 26,000 subjects. Zoloft, now available as generic sertraline, and Lexapro (escitalopram), which is still under patent protection, stood out both by how effective the drugs were at reducing clinical ratings of depression and how well patients tolerated the drugs.

Effectiveness was defined as a 50% reduction in clinical ratings of depression after eight weeks on a drug. The most effective drugs were Zoloft, Lexapro, Remeron and Effexor. Dropout rates were used to assess drug acceptability. Even though people may drop out of a clinical study for any reason, researchers figured a high dropout rate indicated a poorly tolerated drug. Zoloft and Lexapro had the best rates of acceptability.

The findings differ markedly from a similar, U.S.-based review of antidepressants. Published in the Annals of Internal Medicine in November, it examined data from 196 clinical studies and reviews. In contrast with the Lancet review, it concluded that there was no real difference among the drugs in terms of clinical benefit. But there were differences in side effects, and the U.S. study, unlike the Lancet study, itemized these adverse effects.

Among them: Patients on Paxil gained more weight than those on Prozac or Zoloft, and patients on Effexor experienced more nausea and vomiting than those on any of the selective serotonin reuptake inhibitors (SSRIs). Patients on Zoloft had more diarrhea than those on eight other drugs.

Both studies used a statistical technique called meta-analysis to evaluate newer generation antidepressant drugs, including the SSRIs Celexa, Lexapro, Prozac, Luvox, Paxil and Zoloft, and drugs with different actions in the brain, such as Wellbutrin, Cymbalta, Remeron and Effexor. Neither study assessed older tricyclic antidepressants that are not generally used as first-line drugs.

Both studies were done to help doctors choose a drug when treating depressed patients (the U.S. effort led to clinical guidelines for primary care physicians).

And both teams took pains to avoid influence or bias — a tiny minority of authors reported getting research funds or speaking fees from the drug companies that make antidepressants. The European team did its study without funding and the U.S. team’s work was supported by the Agency for Healthcare Research and Quality, a federal agency charged with improving healthcare for Americans.

So why did one study find a difference and the other not? In a word, statistics.

Another difference between the studies is in their interpretation of results. In the Lancet study, for example, Zoloft was 25% more effective than Prozac, found to be statistically significant because of the methodology used. But in the U.S. study, an 11% difference was found and — again, due to methodology — this was not statistically significant.

Another recent study may further confound things, because it concludes that the performance of antidepressants in the medical literature is inflated anyway. A former drug reviewer for the U.S. Food and Drug Administration obtained internal FDA reviews for 12 antidepressants and found that studies with positive results were much more likely to be published in the medical literature than those with marginal or negative results.

The study, published in the New England Journal of Medicine in 2008, found that a drug’s effectiveness as gleaned from published reports was 32% better, on average, than unpublished reports given by companies to the FDA.

What this underscores is that these systematic reviews are only as good as the data they analyze.

All doctors tend to agree that the best drug to combat depression is the one that works, which can vary from person to person.