A systematic review and meta-analysis of clinical studies revealed that cannabis use shrinks brain regions involved in reward, learning and memory. [1][4]
Another systematic review and meta-analysis of clinical studies revealed that cannabis use in adolescence increased depression in young adulthood 37% and suicide attempts by 346% [2]
In Canada 30,000 medical doctors were officially informed that medicinal cannabis use does more harm than good. [3]
Another meta-analysis revealed that cannabis use by people with mental disorders increased violence 3 times. [5]
References
[1] https://link.springer.com/article/10.1007/s00406-019-00979-1
[2] https://jamanetwork.com/journals/jamapsychiatry/article-abstract/2723657
[3] https://www.dailymail.co.uk/health/article-5396693/Cannabis-does-harm-go…
[4] https://www.ncbi.nlm.nih.gov/pubmed/31232216/
[5] https://www.sciencedirect.com/science/article/abs/pii/S0165178118323862