Although there is already significant evidence that marijuana could have a positive effect on PTSD patients, the U.S. Department of Veterans Affairs currently prohibits doctors from prescribing marijuana to patients even in states where it is legal, noting on its website that “controlled studies have not been conducted to evaluate the safety or effectiveness of medical marijuana for PTSD.” This has caused an unknown number of PTSD-affected veterans returning to the U.S. to circumvent the VA system, and also seek out illegal means of purchasing marijuana.