Certainly not huge enough to leave out of the title. The vast majority, potentially 90%, of marijuana users are not at elevated risk of the mental illnesses listed.

For reference, this is a similar percentage of alcoholics among alcohol drinkers. What’s true for someone who drinks a bottle of whiskey every day is not necessarily true of someone who drinks a glass of wine twice a month, and it’s flatly incorrect to say that alcohol use in general carries the same risk as heavy alcohol use.