In 1964, Israeli chemists Gaoni and Mechoulam isolated pure THC from hashish for the first time and determined its exact chemical structure, solving a mystery that had stumped researchers for over a century.
Anyone interested in the origins of cannabis science, the history of drug discovery, or understanding why THC research was delayed for over a century despite cannabis being one of the oldest known psychoactive plants.
2,205+citations from a 2-page paper — one of the most impactful brief communications in the history of chemistry
The Backstory
It was 1963. Morphine had been isolated from opium in 1804. Cocaine from coca leaves in 1855. Mescaline in 1897. Yet somehow, in the second half of the twentieth century, nobody knew the chemical structure of the molecule that made cannabis psychoactive. One of the oldest and most widely used drugs in human history, and science couldn't say what it actually was.
A young chemist in Israel thought that was strange.
The 120-Year Gap
Cannabis had been used medicinally for thousands of years, and Western medicine had formally adopted it in the 1840s after William O'Shaughnessy brought it back from India. But while other plant drugs yielded their secrets to nineteenth-century chemistry, cannabis refused.
The problem was physical, not intellectual. Morphine and cocaine form crystalline salts — neat, solid compounds that chemists can wash, recrystallize, and purify. Cannabis didn't work that way. Its active components were oily, sticky, and nearly impossible to separate from the dozens of other compounds in the plant extract.
Evidence Matrix
A Century of Near-Misses
| Study | Design | N | Finding | |
|---|---|---|---|---|
| ○ | Cahn(1932) | Isolation | — | Determined structure of cannabinol (CBN), but proved it was not psychoactive |
| ↔ | Adams(1940) | Isolation + Synthesis | — | Isolated CBD and crude THC fractions; created synthetic analogs with cannabis-like activity, but could not purify the natural active compound |
| ↔ | Todd(1940) | Isolation | — | Independently isolated CBD in England, confirmed Adams' work, but also failed to isolate pure THC |
| ↔ | Wollner(1942) | Extraction | — | Extracted THC-containing fractions from cannabis, but could not determine the exact structure |
| ↑ | Gaoni & Mechoulam(1964) | Isolation + NMR | — | Isolated pure THC, determined complete structure by NMR spectroscopy, confirmed by partial synthesis |
Pertwee (2006), Br J Pharmacol; Mechoulam (2000), Chem Phys Lipids
Roger Adams at the University of Illinois came closest. In the early 1940s, he isolated CBD, created synthetic compounds that mimicked cannabis effects, and even extracted THC-containing fractions. But he couldn't get pure THC. The oily compound eluded crystallization, and without pure material, the analytical tools of the era couldn't determine its structure.
For twenty years after Adams, nobody solved it.
The Man Who Asked "Why Not?"
Raphael Mechoulam was born in Sofia, Bulgaria, in 1930. His family emigrated to Israel in 1949 to escape persecution. He studied chemistry at Hebrew University of Jerusalem, earned his PhD at the Weizmann Institute with a thesis on steroid chemistry, and completed a postdoc at the Rockefeller Institute in New York.
When he returned to Israel and began looking for a research problem, he was drawn to a striking gap in the literature.
“Morphine had been isolated from opium in the early 19th century. Cocaine had been isolated from coca leaves in the mid-19th century. And here we were, mid-20th century, and yet the chemistry of cannabis was not known.”
— Raphael Mechoulam
Weizmann Institute of Science, Israel
Explaining what drew him to cannabis research
The gap made no sense. Cannabis was one of the most widely used psychoactive substances on the planet. Millions of people were consuming it. Governments were spending enormous resources trying to suppress it. And yet nobody could say what molecule was actually responsible for the high.
Mechoulam decided to find out.
Five Kilograms on a Bus
There was a practical problem first: where do you get cannabis for research? Mechoulam went to the administrative director of the Weizmann Institute and asked if he knew anyone in the police who might help. The director made a phone call. The next day, Mechoulam took a bus to a police station in Tel Aviv and walked out with five kilograms of confiscated Lebanese hashish.
He carried it on the public bus back to Rehovot.
"I was in the bus carrying five kilos of hashish with people saying there was kind of a strange smell," he later recalled.
What neither Mechoulam nor the police investigator realized was that they had both broken the law. You couldn't simply hand over five kilograms of a controlled substance without the proper permits, regardless of the purpose. When the bureaucratic oversight came to light, Mechoulam — then a young and relatively unknown researcher — got off with an apology.
The police continued supplying his lab with hashish for the next forty years.
How They Did It
Mechoulam worked with two key collaborators: Yechiel Gaoni, an organic chemist who performed much of the bench work, and Haviv Edery, a pharmacologist who would later confirm the biological activity of their isolate.
The methodology was elegant — a sequence of increasingly precise separation steps, capped by a chemical trick that solved the crystallization problem no one else had overcome.
How They Did It
From Hashish to Pure THC
Extraction
Crude hashish was extracted with petroleum ether, dissolving the cannabinoids and leaving behind plant material.
Starting material: 5 kg confiscated Lebanese hashish
Column Chromatography
The crude extract was passed through an alumina column with solvents of increasing polarity, separating different cannabinoids into distinct fractions.
This separated THC from CBD, CBN, and other compounds — but THC came out as an oil
Crystalline Derivative
The key innovation. THC was reacted to form a crystalline 3,5-dinitrophenyl urethane derivative — converting the stubborn oil into a solid that could be purified by recrystallization.
This was the step previous researchers couldn't achieve
Hydrolysis and Distillation
The purified derivative was converted back to free THC, then distilled under high vacuum (0.05 mm Hg) at 155-157°C to yield pure compound.
First time pure THC existed in a laboratory
Structure Determination
Nuclear magnetic resonance (NMR) spectroscopy revealed the complete molecular structure. Partial synthesis confirmed the proposed structure independently.
NMR was unavailable to Adams and Todd in the 1940s — this technology made the difference
Gaoni & Mechoulam (1964), J Am Chem Soc 86(8):1646-1647
The compound they identified was (−)-delta-9-trans-tetrahydrocannabinol — a terpenophenolic molecule with 21 carbons, 30 hydrogens, and 2 oxygens. It was the molecule that millions of people had been consuming for millennia without knowing its name.
Molecular Profile
Delta-9-Tetrahydrocannabinol (THC)
Δ9-THC
A terpenophenolic compound and the primary psychoactive constituent of cannabis. Its structure features a dibenzopyran ring system with a phenolic hydroxyl group and a pentyl side chain. The delta-9 designation refers to the position of a key double bond in the cyclohexene ring.
Formula
C₂₁H₃₀O₂
Molecular Weight
314.47 g/mol
Class
Terpenophenolic
Boiling Point
155-157°C (0.05 mmHg)
State
Viscous oil (not crystalline)
Optical Activity
Levorotatory (−)
Gaoni & Mechoulam (1964), J Am Chem Soc
Two Pages That Changed Everything
2,205+
citations from a two-page paper in the Journal of the American Chemical Society — making it one of the most impactful brief communications in the history of chemistry.
For perspective, many influential full-length research articles accumulate fewer than 500 citations over their lifetime.
Semantic Scholar citation data
The paper was just two pages long. Published April 1, 1964, in the Journal of the American Chemical Society — one of the most prestigious chemistry journals in the world. It reported the isolation, structural determination, and partial synthesis of delta-9-THC. No pharmacology, no clinical observations, no speculation about medical applications. Just clean, definitive chemistry.
The year before, Mechoulam's lab had already determined the structure of cannabidiol (CBD). The year after, they achieved the total synthesis of both THC and CBD — creating the molecules from scratch in the laboratory, proving beyond any doubt that their structural assignments were correct.
What Mechoulam Actually Did (and Didn't Do)
Myth vs. Reality
Raphael Mechoulam discovered THC in 1964.
Mechoulam and Gaoni isolated pure THC and determined its exact molecular structure. Roger Adams and others had identified THC-containing fractions in cannabis as early as 1940, but couldn't purify the compound or determine its structure.
The Evidence
Adams created synthetic analogs with THC-like activity in the early 1940s, confirming that something like THC existed. What he lacked was NMR spectroscopy (not yet available) and the derivatization technique Mechoulam invented to crystallize the oily compound. Mechoulam himself has not claimed to have 'discovered' THC — the distinction matters.
Adams (1940), J Am Chem Soc; Gaoni & Mechoulam (1964), J Am Chem Soc
The distinction between "discovering" and "characterizing" is not pedantic — it's central to understanding why the 1964 paper mattered. Adams knew something like THC existed. What Mechoulam provided was the exact molecular blueprint: the precise arrangement of every atom, the stereochemistry, the structure-activity relationship. Without that blueprint, you couldn't make synthetic versions, you couldn't design receptor studies, you couldn't develop drugs. The structure was the key that unlocked everything that followed.
The Cascade
This is why the 1964 paper is ranked number one. Not because of what it reported — the structure of a single molecule — but because of what it made possible. Every major discovery in cannabinoid science traces back to this structural identification.
Research Timeline
From One Molecule to an Entire Biological System
Cannabinol (CBN) first isolated from cannabis
First phytocannabinoid identified, but not psychoactive
Roger Adams isolates CBD; creates synthetic THC analogs
Proved something like THC existed, but couldn't isolate or characterize it
Mechoulam determines the structure of CBD
First complete structural characterization of a major cannabinoid
Gaoni & Mechoulam isolate and characterize THC
The breakthrough — the active molecule is finally identified
Total synthesis of THC and CBD achieved
Confirmed the structures and enabled synthetic production for research
Allyn Howlett shows THC acts through specific receptors
Proved cannabinoids don't just dissolve into membranes — there's a lock for this key
CB1 receptor cloned by Tom Bonner's lab (NIH)
The receptor THC binds to in the brain is identified at the genetic level
Anandamide discovered by Devane & Mechoulam
The brain makes its own THC-like molecule — the endocannabinoid system exists
CB2 receptor cloned by Sean Munro (Cambridge)
A second cannabinoid receptor found, primarily in immune cells
2-AG discovered (Mechoulam's lab)
The second major endocannabinoid identified — more abundant than anandamide
FDA approves Epidiolex (CBD) for epilepsy
First cannabis-derived drug approved by FDA — direct descendant of Mechoulam's work
Pertwee (2006), Br J Pharmacol; Mechoulam & Parker (2013), Annu Rev Psychol
The logic is direct: you can't study how a drug works if you don't know what the drug is. Once Mechoulam identified THC's structure, researchers could synthesize labeled versions to trace where it goes in the body. That tracing led Allyn Howlett to discover that THC binds to specific receptors — not randomly, but with precision. That led to the cloning of those receptors. And the existence of dedicated receptors raised the obvious question: why would the brain have receptors for a plant molecule?
The answer — the endocannabinoid system — turned out to be one of the most important regulatory systems in human biology, governing mood, appetite, pain, memory, and immune function. All from a two-page chemistry paper.
The Man Behind the Molecule
Mechoulam continued working for nearly sixty years after the THC paper. He co-discovered anandamide — the brain's own cannabis-like molecule — in 1992, and 2-AG in 1995. He received the Israel Prize in Chemistry, the Rothschild Prize, and the Heinrich Wieland Prize, among dozens of other honors.
“We looked for a Hebrew name, but as you may well be aware, Jews are not very happy. We have a lot of words for being down and so on, but not so many words for extreme joy.”
— Raphael Mechoulam, 1992
On why they chose the Sanskrit word 'ananda' (bliss) to name anandamide
Despite dedicating his life to cannabis chemistry, Mechoulam never used cannabis himself. He described his research as "an addiction from which he did not want to be cured."
He was also haunted by the slow translation of his findings into medicine. His lab had demonstrated CBD's anti-epileptic potential as early as 1980, in collaboration with researchers in Sao Paulo, Brazil. It took more than 35 years for the first CBD epilepsy drug to reach patients.
“Who cared about our findings? No one! Did we have to wait 30 years? We could have helped thousands of children, and we didn't!”
— Raphael Mechoulam
On the decades-long delay between his CBD epilepsy research and the approval of Epidiolex
Mechoulam died on March 9, 2023, in Jerusalem, at the age of 92. He had been working until weeks before his death.
What It Means Today
Every cannabis product sold today — every labeled THC percentage, every drug test for THC metabolites, every medical marijuana prescription — depends on the structural identification Mechoulam and Gaoni published in 1964.
More broadly, the discovery of the endocannabinoid system has opened therapeutic avenues far beyond cannabis itself. Researchers are now developing drugs that target the ECS for conditions ranging from chronic pain to anxiety to neurodegenerative disease — none of which would be possible without first knowing what THC is and how it works.
Israel, where Mechoulam did his work, now has over 123,000 patients licensed for medical cannabis — roughly 1 in 73 citizens. The country imports more medical cannabis than any other nation.
Related Research
The Studies That Followed
Mechoulam's 1964 THC isolation set off a chain of discoveries that transformed our understanding of the brain and body.
Isolation and structure of a brain constituent that binds to the cannabinoid receptor
Devane, Hanus, Mechoulam et al. (1992)
The discovery of anandamide — the brain's own THC. Mechoulam's second landmark paper.
Cloning the CB1 receptor
Matsuda et al. (1990)
Identified the gene for the receptor THC binds to in the brain.
Gi signaling in cannabinoid responses
Howlett et al. (1986)
Cell experiments linked cannabinoid responses to Gi-dependent signaling.
The endocannabinoid system: body's own cannabis
Mechoulam & Parker (2013)
Mechoulam's masterwork review — 50 years of perspective on what his discovery wrought.
Did Mechoulam discover THC?
More precisely, Mechoulam and Gaoni isolated THC in pure form and determined its exact chemical structure. Roger Adams and others had identified THC-containing fractions in the 1940s, but could not purify the compound or determine its structure due to technological limitations. Mechoulam's breakthrough was achieving pure isolation using a novel derivatization technique and confirming the structure with NMR spectroscopy.
Why did it take until 1964 to identify THC when morphine was isolated in 1804?
Unlike morphine and cocaine, which form crystalline salts that are easy to purify, THC is an oily compound that resists crystallization. Earlier researchers could not separate pure THC from the complex mixture of cannabinoids in cannabis extract. Mechoulam's innovation was converting THC to a crystalline derivative for purification, then using nuclear magnetic resonance — a technology not available to earlier researchers — to determine the structure.
What the researchers found
The psychoactive constituent of cannabis (hashish) was isolated in pure form for the first time and identified as (−)-delta-9-trans-tetrahydrocannabinol (Δ9-THC). Its structure was determined by NMR spectroscopy and confirmed by partial synthesis. The compound was extracted from 5 kg of Lebanese hashish using petroleum ether extraction, alumina column chromatography, and a crystalline 3,5-dinitrophenyl urethane derivative technique that allowed purification of the otherwise oily compound.
Why it matters
This paper solved a 120-year-old mystery in pharmacology. While morphine was isolated from opium in 1804 and cocaine from coca leaves in 1855, the psychoactive molecule in cannabis remained unidentified until 1964. The structural determination of THC made it possible to study how cannabis works in the body, directly leading to the discovery of cannabinoid receptors (1988-1990), the endocannabinoid system (1992), and the development of cannabinoid-based medicines including dronabinol, nabilone, Sativex, and Epidiolex.
How the study worked
The researchers extracted 5 kg of confiscated Lebanese hashish with petroleum ether, then separated the crude extract using alumina column chromatography with progressively polar solvents. The key innovation was converting the oily THC into a crystalline 3,5-dinitrophenyl urethane derivative, which could be purified to homogeneity. The purified derivative was hydrolyzed back to THC and distilled at 155-157°C under 0.05 mm Hg vacuum. Structure was determined using nuclear magnetic resonance (NMR) spectroscopy — technology unavailable to earlier researchers. Partial synthesis confirmed the proposed structure.
What this study cannot tell us
This was a chemistry paper focused on isolation and structural characterization, not pharmacology or clinical effects. The starting material was confiscated hashish of uncontrolled origin. No biological activity assays were performed in this specific paper (pharmacological confirmation was published separately by collaborator Haviv Edery). The study characterized only delta-9-THC and did not address other cannabinoids present in the extract beyond noting their chromatographic separation.
How to read the evidence
Rated strong because this is a definitive chemistry result — the structural characterization has been confirmed by thousands of subsequent studies and total synthesis. The methodology is sound and reproducible. While this is not a clinical study, it is the foundational observation that enabled all subsequent cannabis pharmacology.
When this study was published
Published in 1964, this is a 62-year-old paper. Its age is part of its significance — it represents the starting point of modern cannabinoid science. The chemistry has been repeatedly confirmed and the structure of THC is now one of the most well-characterized molecules in pharmacology.
The bigger picture
The isolation and structural characterization of THC is the foundational event of modern cannabinoid science. Without knowing THC's structure, researchers could not create synthetic analogs, develop receptor binding assays, or understand how cannabis interacts with the brain. This single paper set in motion a chain of discoveries: cannabinoid receptor identification (Howlett, 1988), CB1 receptor cloning (Matsuda/Bonner, 1990), anandamide isolation (Devane/Mechoulam, 1992), CB2 receptor cloning (Munro, 1993), and 2-AG discovery (1995). The entire endocannabinoid system — now recognized as one of the most important regulatory systems in human physiology — was discovered because Mechoulam's team identified what THC actually is.
Questions still open
- If THC is the primary psychoactive compound, what roles do the other 100+ cannabinoids play?
- Why does the brain have receptors for a plant molecule — could there be an endogenous equivalent?
- Can the structure of THC be modified to create therapeutic compounds without psychoactivity?
Common questions
Did Mechoulam discover THC?
Why did it take until 1964 to identify THC when morphine was isolated in 1804?
Read the original research
Isolation, Structure, and Partial Synthesis of an Active Constituent of Hashish
Journal of the American Chemical Society, 86(8), 1646-1647
Citation
Gaoni, Y; Mechoulam, R. (1964). Isolation, Structure, and Partial Synthesis of an Active Constituent of Hashish. Journal of the American Chemical Society, 86(8), 1646-1647. https://doi.org/10.1021/ja01062a046