After giving written informed consent, participants will undergo screening for initial eligibility. Potential participants will be required to stop using non-study medical cannabis for two weeks during screening, and for the duration of the study if enrolled. After the two-week washout, a blinded independent rater will administer the Clinician-Administered PTSD Scale (CAPS-5) to assess presence and severity of PTSD symptoms. Self-report measures will also be completed. Eligible participants will then be enrolled and randomized. In the active portion of the study, participants will receive two of four different types of cannabis during two stages (Stage 1 and Stage 2), each lasting three weeks, with crossover and re-randomization at Stage 2. Prior to each stage, participants will complete two introductory sessions where they will be trained on cannabis self-administration. During each stage, participants will be provided 1.8 grams of cannabis daily to smoke ad libitum. Each stage will be followed by a two-week cessation. To reduce the risk of diversion, after the second cessation period, participants will have the option to complete a third stage of the study where they can request the remaining unused cannabis from either Stage 1 or 2. All participants will complete a six-month follow-up after completion of the experimental portion of the study.