A study found that cannabinoid receptor antagonists, a relatively new class of weight loss drugs, stunted the brains of juvenile mice. It is possible that such drugs could have similar effects on human children.

Several new anti-obesity treatments, including Merck's taranabant and rimonabant -- sold in Europe as Acomplia -- reduce appetite by blocking the brain's cannabinoid receptors. But they also have disturbing side effects that are only now becoming apparent.

Other researchers have found that cannabinoid receptor blockers interfere with neural connectivity in rat brains -- a phenomenon associated with depression in humans. The FDA has so far refused to approve Acomplia because it appears to cause anxiety, depression and suicidal thoughts.