The purpose of this study is to assess the effectiveness, safety and tolerability of Cannabidiol in patients with bipolar depression (BD I or BD II) who have not responded to adequate trials with at least one first-line treatment for bipolar depression in comparison to those who will be treated with placebo.

Participants will come in for a screening visit to be interviewed about their medical and psychiatric history, as well as have clinical blood tests done to confirm eligibility for the study. Participants found to be eligible will come in for a baseline visit to be randomly allocated to receive either CBD or placebo for the next 6 weeks, and return to the clinic 3 more times for clinical assessments, blood samples, and neurocognitive testing.