. . . [T]he legalization of medical marijuana is associated with a 5 percent decrease in the total suicide rate, an 11 percent decrease in the suicide rate of 20- through 29-year-old males, and a 9 percent decrease in the suicide rate of 30- through 39 year-old-males. Estimates for female suicide rates are generally measured with less precision and are sensitive to functional form.
That is from the paper "High on Life? Medical Marijuana Laws and Suicide" by Anderson, Rees, and Sabia.
An interesting graph from the paper: