Irritability, anxiety and physical tension, plus decreases in appetite and mood, were experienced by regular marijuana users who quit the drug for four weeks during a study conducted at McLean Hospital in Belmont, Mass. Sixty percent of those in the study experienced “significant symptoms” of withdrawal, said the researchers, Elena M. Kouri and Harrison Pope. Kouri and Pope are Harvard researchers. “Most people think marijuana is a benign drug, and there is disagreement in the scientific community about whether withdrawal causes significant symptoms. This study shows that using marijuana for a long time has consequences,” said Kouri.