The history of cannabis regulation in the United States is not a straight line from prohibition to reform. Cannabis was a legal, commercially available medicine before it was banned, and the ban arrived through a mechanism that never quite said what it was doing.
Cannabis as a Listed Medicine
Cannabis entered Western medicine substantially through William Brooke O’Shaughnessy, an Irish physician working in Calcutta in the 1830s. He studied its use in Indian medicine, conducted his own trials, and published on its application to conditions including rheumatism, tetanus and convulsions — including a case of infantile convulsions that drew considerable attention.
His work brought cannabis into British and then American medical practice. By the second half of the nineteenth century it was a standard pharmacy item, listed in the United States Pharmacopeia and sold by major pharmaceutical manufacturers as tinctures and extracts for pain, sleep, appetite and muscle spasm.
Its decline in medical use began before any legal restriction. Injectable opiates and, later, aspirin offered more predictable dosing — cannabis preparations varied enormously in strength, which is precisely the problem that potency testing exists to solve.
The 1937 Marihuana Tax Act
The federal turn came in 1937. The Marihuana Tax Act did not formally prohibit cannabis — it imposed a tax and a registration requirement on anyone dealing in it, with penalties for non-compliance severe enough that the practical effect was prohibition.
The legislative record around it is not edifying. The campaign leading to the Act relied heavily on sensational press coverage, and the terminology itself — “marihuana” rather than the cannabis familiar to physicians and pharmacists — did work that was partly deliberate. Racial politics of the period were explicitly present in the advocacy.
The American Medical Association opposed the Act, objecting both to the restriction on a medicine still in use and to the process by which it was passed.
Cannabis was removed from the United States Pharmacopeia in 1942. Within five years it went from a listed medicine to a substance most physicians could not practically prescribe.
The Controlled Substances Act
The Marihuana Tax Act was struck down in 1969 on constitutional grounds — the registration requirement compelled self-incrimination. Congress responded with the Controlled Substances Act of 1970, which placed cannabis in Schedule I: the category reserved for substances deemed to have high abuse potential and no accepted medical use.
Schedule I is the foundation of everything since. It is why cannabis research has been difficult to conduct, why federal agencies have no framework for regulating cannabis products, why banks avoid the sector, and why state programmes exist in tension with federal law rather than under it. Practical consequences are covered in why dispensaries still operate in cash.
States Move First
Reform came from the states, and it came slowly.
California’s Proposition 215 in 1996 was the first medical cannabis programme in the modern era. Over the following two decades a majority of states followed with medical frameworks, and from 2012 onward a growing number added adult-use legalisation.
Each state built its own system — its own eligibility rules, licensing structure, product standards and testing requirements — because there was no federal framework to build on. That is the direct cause of the patchwork described in how testing rules differ across states.
The Case That Changed the Conversation
Public opinion shifted for many reasons, but one case did disproportionate work.
Charlotte Figi was a Colorado child with Dravet syndrome, a severe treatment-resistant epilepsy. Her family’s use of a high-CBD, low-THC cannabis extract, and the reported reduction in her seizures, received national coverage in 2013. The strain was renamed Charlotte’s Web.
The effect on policy was rapid and specific: a wave of states that had shown no interest in broad medical cannabis passed narrow CBD-only laws. It also refocused attention on CBD as distinct from THC and, importantly, on product consistency — families were dosing a child with an unregulated preparation, and that made composition testing a mainstream concern rather than a technical one. The fuller account is in Charlotte Figi and the turning point for CBD.
Hemp Splits Off
The 2018 Farm Bill removed hemp — cannabis containing no more than 0.3% delta-9 THC by dry weight — from the Controlled Substances Act.
That created two parallel legal categories for what is botanically one plant, distinguished by a threshold. It also created the CBD retail market and, less intentionally, a market in hemp-derived intoxicating cannabinoids that the drafters did not anticipate. See CBD oil in Oklahoma.
Oklahoma’s Route
Oklahoma legalised medical cannabis by ballot initiative in 2018 — State Question 788 — with an unusually permissive framework. No cap on business licences, and no list of qualifying conditions, leaving the recommendation to the physician’s judgement.
The programme has been substantially revised since. Oversight was consolidated under the Oklahoma Medical Marijuana Authority as a standalone agency, testing requirements tightened to include ISO/IEC 17025 accreditation for laboratories, a moratorium on new business licences was introduced to let enforcement catch up, and from January 2026 physicians recommending cannabis must be registered with OMMA and complete approved education.
That arc — permissive framework, rapid growth, then progressive tightening — is close to universal across legalising jurisdictions. Current requirements are in Oklahoma cannabis testing requirements, and the market history in Oklahoma’s cannabis market.
What the History Suggests
Two things stand out.
First, cannabis was regulated out of medicine largely for reasons unrelated to evidence, and rebuilding an evidence base has taken decades — partly because Schedule I made the research itself difficult. That is why the state of the evidence is patchier than the length of the plant’s medical history would suggest. See the science behind medical cannabis research.
Second, the nineteenth-century problem and the modern one are the same problem. Cannabis preparations varied unpredictably in strength, which limited their clinical usefulness then and drives the testing requirements now. The difference is that we can now measure what is in a product. That capability is what separates a regulated cannabis market from an unregulated one — as much as any statute.