Cannabis timeline · 1800 to 1936
Medicine and early law
4 milestones from 1839 to 1925: o'Shaughnessy publishes his Indian hemp experiments; cannabis enters the US Pharmacopoeia; the first US state cannabis laws; and more.
1839
O'Shaughnessy publishes his Indian hemp experiments
An Irish physician in India published experiments with hemp preparations, reporting possible uses against convulsions and tetanus. His work helped start cannabis medicine in Britain.
1850
Cannabis enters the US Pharmacopoeia
Cannabis was first listed in the United States Pharmacopoeia in 1850, in an era when it was widely sold in patent medicines.
1911–1913
The first US state cannabis laws
Massachusetts passed one of the earliest state cannabis laws in 1911 or 1912, and California, Maine, Indiana and Wyoming followed in 1913.
Sources differ on the Massachusetts year and on whether it was a ban or a prescription rule.
1925
The Geneva Convention adds Indian hemp
An international opium treaty signed in Geneva added Indian hemp to its trade controls, requiring import certificates that state a medical or scientific need.
Written from the listed sources. Not legal or medical advice. Reviewed October 19, 2026.