The Study That Identified THC — The Molecule That Makes Cannabis Psychoactive
Isolation, Structure, and Partial Synthesis of an Active Constituent of Hashish
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.
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.
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.
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.
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.
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.
Frequently Asked Questions
Cite this study
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