A JAMA analysis questioning the effectiveness of antidepressants has renewed debate.

The meta-analysis found that antidepressents are useful for those with severe depression symptoms but don’t work any better than placebo in mild cases. In a letter to The New York Times, Weill Cornell psychiatry professor Dr. Richard Friedman derided the research for including only two drugs and for excluding studies that screened out placebo responders.

Two of the researchers defended their methodology, saying many approved antidepressants vary little in effectiveness and that their aim was to estimate effects of medications vs. placebos.