Rats who were dosed with a chemical similar to marijuana for 20 days had symptoms of depression and anxiety in adulthood, according to a study published December 5 in the journal Neurobiology of Disease.

Though a recent long-term study in humans exonerated marijuana as a risk factor for suicide, questions do remain about its impact on psychological well-being.

To determine marijuana’s effect on the developing brain, Francis Rodriguez Bambico, PhD, and her colleagues at McGill University in Montreal, gave adolescent and adult rats a chemical that acts on the same brain receptors as marijuana for 20 days. Though there were no symptoms of psychological distress in the adult rats, the adolescent rats displayed signs of depression after low doses of the chemical and anxiety after high doses when they reached adulthood.

The authors conclude that their research might indicate long-term marijuana use in adolescence could have lasting negative effects on mental health in adulthood.