Cannabis and the United States military

[1] During World War I, military doctors recommended that the American Expeditionary Force carry cannabis indica tablets to treat headaches, insomnia, and cramps.

[2] Some of the earliest reports of recreational cannabis use in the military came from the Panama Canal Zone in 1916, where troops were noted to be using the drug.

[3][4] Also in 1916, thousands of US troops used marijuana while in Mexico on General John Pershing's punitive expedition against Pancho Villa (1916–1917).

[5] In 1921, the commanding officer of Fort Sam Houston in San Antonio, Texas, prohibited the use of cannabis on the base.

Initially rates of usage among deployed soldiers were comparable to those of their stateside peers, with 29% of troops departing Vietnam in 1967 reporting having ever used marijuana in their lives.