Answer:

1. Prehistoric Chinese corpse from 2400-2800 B.C., found shrouded and entombed in cannabis leaves. Archeologists found similar cannabis fragments in other tombs leading them to believe that “cannabis was used by the local central Eurasian people for ritual and/or medicinal purposes” during this time.

Prehistoric body found buried in cannabis-plant shroud at ancient Silk Road oasis | The Independent | The Independent

2. The first documented medical use of Cannabis also occurred in China around

2900 B.C. when Chinese Emperor Fu Hsi, noted that "Ma," the Chinese word for Cannabis, was a "very popular medicine that possessed both yin and yang." The "Pen ts'ao," a Chinese digest of herbal medicines, first published in or about 2800 B.C., "recommended Cannabis for the treatment of constipation, gout, malaria, rheumatism, and menstrual problems.

10,000-year History of Marijuana Use in the World, ADVANCED

HOLISTIC HEALTH, http://www.advancedholistichealth.org/history.html

3. Cannabis plant spread throughout the world. By 2000 AD, ancient Egypt used fiber for sail cloth and for medical uses.

Claire Rankin, Marijuana use in ancient Egypt, (Feb. 26, 2016),

Marijuana use in ancient Egypt (newstarget.com)

see also In the Matter of Rescheduling Marijuana, 86-22 at p. 33 (1988) (in a proceeding contested by the DEA, the ALJ observed: "Uncontroverted evidence [o]n this record indicates that marijuana was being used therapeutically by mankind 2000 years before the Birth of Christ".

4. In around 500 BCE, the ancient Greek historian Herodotus described people near the Caspian Sea gathering in small, enclosed tents to breathe in the smoke from cannabis burned atop a bowlful of red-hot stones.

https://arstechnica.com/science/2019/06/oldest-evidence-of-cannabis-smoking-found-in-ancient-chinese-cemetery/?comments=1

5. Sold as a tincture in the late 1800s and early 1900s' over the counter in barbershops and apothecaries
6. Cannabis formally introduced by William O'Shaunessy into Western medicine in 1830's in the form of tinctures and in raw form which was sold in barbershops and apothecaries.

Martin Booth, CANNABIS: A HISTORY 109-10 (2003); Steve DeAngelo, THE CANNABIS MANIFESTO: A NEW PARADIGM FOR WELLNESS 48 (2015).

7. 1870 – 1920s - Domestic Migration of former slaves and Mexican migrants and the spread of cannabis.