Hemp | Plant Medicine From Rome thru Jerusalem to now

One species, many, many lives.

Hemp is Cannabis sativa L. So is the plant that gets you high, and so is the plant that becomes rope. One species, bred into lives that look unrelated: a stalk grown for fibre, sometimes to four metres — the word canvas descends from cannabis — and a squat, resin-heavy flower bred toward a single molecule. The woodcut above is 1543, hemp as it was known for most of its history: a crop of fibre and seed.

Extracts pressed from hemp plants vary widely by genetics and the life a plant leads before harvest. All of that goes into a plant's chemistry: which cannabinoids it makes, in what proportion, alongside which terpenes. For instance, many cannabis sativa strains produce little to no psychoactive THC in their lifecycle.

Strain names themselves are a looser guide than they look — researchers who genotyped 14,031 markers across 81 marijuana and 43 hemp samples found the names "often do not reflect a meaningful genetic identity",^[3] a finding later work confirmed.^[4]

The fork every cannabis plant inherits

That chemistry comes down to a fork. Every cannabis plant builds its cannabinoids from a single precursor, CBGA — fairly called the mother cannabinoid — and then routes it. Inherit one enzyme, CBDA synthase, and the plant sends CBGA toward CBD. Inherit the other, THCA synthase, and the same raw material goes toward THC. Inherit both and it makes a measure of each.^[5] This is why CBD leads in some plants and barely registers in others — the branch the plant was born onto, settled at the seed.

Sort plants by that fork and a handful of chemical types emerge. THC-dominant plants, grown to be smoked. CBD-dominant plants, where CBD leads and THC stays at a trace. Balanced plants carrying both. Fibre plants running almost pure stalk — the rope from the first paragraph. One species, several chemical destinies.

Which makes the line between "hemp" and "marijuana" a legal one. In US law it is a number: 0.3% Δ9-THC by dry weight.^[6] Below it the plant is legally hemp, above it legally marijuana.

The lock before the key

None of this was knowable before 1964. One laboratory changed that.

That year, at the Weizmann Institute, Raphael Mechoulam and Yechiel Gaoni isolated tetrahydrocannabinol and worked out its structure — the first time anyone established what the active compound in this plant was. Mechoulam got the material from the Israeli police: he asked, and was handed five kilograms. He was thirty-four.

Then in 1990, a group at the National Institute of Mental Health cloned a receptor in rat brain that responded to those exact compounds^[14].

Another receptor — outside the brain — was then characterised in spleen & immune tissue in Cambridge three years later.^[15] All mammals were found to carry two receptors shaped to fit a molecule from a plant most would never encounter. Different locks were being found by experimenting with same key.

Mechoulam's laboratory kept going. In 1992 William Devane, Lumír Hanuš and Mechoulam isolated a compound from pig brain that also bound to those receptors and named it anandamide, from the Sanskrit ānanda: bliss.^[16]

Three years later the same group found a second compound, 2-arachidonoylglycerol — 2-AG.^[17]

They had discovered endocannabinoids, compounds the body makes itself, that bind to the receptors as needed, a network nobody suspected until a plant led them to it, and is still named after that plant. We still think its the worst name ever, because people who disdain cannabis can easily disdain a system in their bodies that works everyday whether you use products made from hemp or not.

Mechoulam worked on it for five more decades and died in 2023, at ninety-two. Most of endocannabinoid science and today's medical cannabis world itself descends from five kilograms of confiscated hashish and this chemist who wanted to know what was in it.

The system runs through the skin

The network is not confined to the brain and the gut, where it was first found. Skin is the largest organ in the body, and it carries a dense share of it.

In 2005 a group in Münster mapped where the receptors sit in human skin. CB1 and CB2 turned up almost everywhere the tissue does its work — on the keratinocytes of the epidermis, on the hair follicles, on the sebaceous and sweat glands, on the skin's own mast cells and macrophages, and on the nerve fibres threaded through all of it. In the epidermis and the glands the two sat in a complementary pattern, the tissue in effect dividing the labour between them.^[7]

And the skin does not only receive these signals. It makes them. Cutaneous cells produce their own endocannabinoids — anandamide and 2-AG, the same molecules the brain runs on — and carry the full set of enzymes to build them and break them down. A loop that runs locally, not an outpost of the system in the brain. A review four years later drew the findings together into a cutaneous endocannabinoid system,^[8] a subject in its own right, and one researchers took to calling the "c(ut)annabinoid" system.^[9]

What it governs is ordinary skin housekeeping: how quickly keratinocytes divide and mature into the barrier,^[10] how much oil the sebaceous glands release,^[11] where the hair-growth cycle sits, how the nerve endings read heat, pressure and itch. It behaves less like a switch than a thermostat — and when researchers disabled it in animals, the skin's inflammatory response ran hotter, not cooler, which is the mark of a brake rather than an accelerant.^[12]

One detail matters for anything applied to the surface. CB2, the receptor most tied to inflammation, sits out here — on the immune cells and the glands, well away from the brain. A compound can meet it at the skin without entering the bloodstream or crossing into the head. Peripheral by design.

That work is now twenty years old and uncontested. It is why a botanical applied to skin is a coherent proposition rather than a fashionable one — the receptors are already there, and a system built to use them.

Getting through

All of that sits under a barrier built to keep things out.

The stratum corneum is the top fraction of a millimetre — dead, flattened cells packed in a matrix of ceramides, cholesterol and free fatty acids. In 1983 Peter Elias proposed the model that has held ever since: two compartments, with the barrier belonging not to the cells but to the lipid between them.^[18] Bricks and mortar is the shorthand that followed. It is why skin works, and why most of what is put on it stays on it.

What crosses does so on two conditions. Small, and oily. The working ceiling, drawn from the drugs and contact allergens that are known to get through, sits near five hundred daltons — above that, dermatologists argue, molecules simply do not pass the corneal layer.^[19] Cannabidiol is 314. β-caryophyllene is 204. Both are far more at home in fat than in water, which is the second condition, and which decides the route: through the mortar, not the bricks.

There is a second door. Hair follicles run straight down through the barrier, and a Berlin group showed in 2008 that closing them off measurably slows what reaches the skin — the follicle is a shunt, not a detail.^[20] Worth noting where that leaves things: the follicle and its sebaceous gland are among the most densely receptor-populated structures in the whole organ. The fastest way in happens to end where the system is thickest.

And the mortar is not fixed. In 1991 two pharmacists at Bradford ran a series of terpenes against 5-fluorouracil, measuring how much more of it crossed human epidermis with each one present.

5-FU is a chemotherapy drug, and it appears here for none of the reasons it is usually named. It is water-loving, it crosses skin badly, and that is exactly why they chose it: if a terpene can move that, the terpene is doing something real to the barrier.

α-Pinene doubled it. 1,8-cineole, the terpene that dominates eucalyptus, raised it nearly ninety-five-fold^[21]. The terpenes were not carrying anything through. They were loosening the lipid the molecule had to cross.

Which is another thing terpenes turn out to do well.

Why the whole plant?

The instinct in lab 7 industry is to isolate: find the active molecule, purify it, discard the rest. It is a clean idea, and for CBD it runs into a strange result. Purified CBD, on its own, works only inside a narrow dose window — too little does nothing, too much does nothing, and the useful range is a sliver.

Add the rest of the plant back and the window opens.

In animals, a whole-plant CBD-rich extract stayed active across a broad dose range where purified CBD did not.^[15] In a 2018 review of more than six hundred patients, those using whole-plant extracts reported benefit at roughly a quarter of the dose, and with fewer side effects, than those on purified CBD.^[16]

The working name for this is the entourage effect — the idea that the plant's compounds do more together than any one of them does alone.^[17] It is a hypothesis with real support and real gaps; it is being refined, not closed. But the direction of the evidence is steady, and it points the opposite way from isolation.

Which is roughly where Pliny began two thousand years ago — with the whole root, simply applied.