Psychiatric symptoms caused by cannabis constituents: a systematic review and meta-analysis
Review of 15 studies found that following administration to healthy individuals, THC significantly increased total symptom severity of psychiatric symptoms vs placebo (standard mean change 1.10, p<0.0001), as well as positive symptoms severity and negative symptom severity.
Source:
The Lancet Psychiatry
SPS commentary:
A related commentary states that healthcare professionals have enough evidence to warn people that using THC could increase their risk of developing psychiatric symptoms or even a psychotic illness.