There isn't evidence linking cannabis to suicide or self-harm. There have been some reviews of it, and the conclusions of the reviews are that there is no way to make that causal association. People who suffer with PTSD and anxiety are at high risk of self-harm and suicide, and they're also more likely to use cannabis, but there is not a link with cannabis causing suicidality.
On February 27th, 2019. See this statement in context.