"The atypical antipsychotic drug cariprazine (sold under the name Vraylar in the US) is currently approved by the US Food and Drug Administration for the treatment of schizophrenia and manic or mixed episodes of bipolar disorder. Based on recent successful phase 3 trials in bipolar depression, the pharmaceutical companies that produce cariprazine, Allergan and Gedeon Richter, plan to apply for a change in FDA labeling later this year to reflect the drug’s apparent ability to treat bipolar depression as well.While many drugs can prevent or treat mania, treating bipolar depression has typically been more of a challenge. The most recent 6-week trial of cariprazine in 493 patients showed that a dose 1.5mg/day was significantly more effective than placebo at reducing depression ratings. (A dose of 3mg/day did not show superiority over placebo as it had in previous trials of cariprazine.)Side effects reported in the trial were mild and included restless legs, nausea, and fatigue. Five percent of those who received cariprazine discontinued the drug due to side effects, compared to three percent of those who received placebo.The mechanism by which cariprazine improves depression is not yet clear. The drug is a dopamine partial agonist, but unlike aripiprazole (Abilify) and brexpiprazole (Rexulti), which have more potent effects on D2 receptors than on D3 receptors, cariprazine is more potent at dopamine D3 receptors. Whether this difference accounts for the positive effects in bipolar depression that aripiprazole and brexpiprazole do not have remains to be seen.