Veterans

At high, but not low levels of PTSD symptoms, more days using marijuana predicted increased PTSD symptoms over time and the likelihood of suicidal behavior.
Conclusions
Results suggest marijuana, especially for military personnel experiencing elevated PTSD symptoms may negatively impact suicidal thoughts and behavior. 

This study of 3,233 veterans in a cross-sectional, multi-site study by the VA found that cannabis use disorder (CUD) was significantly associated with both current suicidal ideation and lifetime suicide attempts compared to veterans with no lifetime history of CUD.

Recent research has documented high rates of comorbidity between cannabis use disorders and posttraumatic stress disorder (PTSD) in veterans.
Overall, 14.6% of participants reported using cannabis in the past 6 months. After controlling for age, race, service era, and combat exposure, past 6-month cannabis use was associated with unmarried status, use of tobacco products, other drug use, hazardous alcohol use, PTSD severity, depressive symptom severity, and suicidality. The present findings show that cannabis use is quite prevalent among veterans seeking PTSD specialty treatment and is associated with poorer mental health and use of other substances.

Marijuana use for medical conditions is an issue of growing concern. Some Veterans use marijuana to relieve symptoms of PTSD and several states specifically approve the use of medical marijuana for PTSD. However, controlled studies have not been conducted to evaluate the safety or effectiveness of medical marijuana for PTSD. Thus, there is no evidence at this time that marijuana is an effective treatment for PTSD. In fact, research suggests that marijuana can be harmful to individuals with PTSD.