Terpenes

Terpenes are built from isoprene, a five-carbon unit. Chain two together and you get a monoterpene with ten carbons: myrcene, limonene, pinene, linalool. Chain three and you get a sesquiterpene with fifteen: caryophyllene, humulene. That is the whole structural story.

Plants make them in the same glandular trichomes that produce cannabinoids, and they make them for reasons that have nothing to do with people. Terpenes deter insects, attract pollinators, and provide some protection against heat and UV. The smell is a side effect of chemical defence.

Because they are volatile, they leave. A jar of flower opened repeatedly loses terpenes to the air. Extraction with high heat loses them too, which is why some producers reintroduce terpenes after extraction rather than preserving them through it. Whether those are cannabis-derived or botanical terpenes is a fair question to ask a brand, and the answer is not always on the label.

Myrcene is usually the most abundant terpene in cannabis and hemp. Earthy and musky, also present in hops, mango and lemongrass. It is the terpene most often associated with sedation, on evidence discussed below that is weaker than its reputation.

Limonene smells like citrus peel, because it is the same compound that makes citrus peel smell that way. Studied for mood effects in animal models and widely used as a solvent and food additive.

Beta-caryophyllene is peppery and woody, and it is the most interesting one pharmacologically. Also in black pepper, cloves and rosemary.

Linalool is the floral note in lavender. It is among the most studied terpenes in isolation, largely in the context of aromatherapy research, which has its own methodological problems.

Alpha-pinene smells like pine resin and is one of the most abundant terpenes in the natural world. Studied for effects on alertness.

Humulene is the hops terpene, earthy and slightly bitter, and it shares a biosynthetic relationship with caryophyllene.

Terpinolene is the least common of the seven, fresh and slightly floral, with a smell people often describe as apple or nutmeg. It is a marker terpene for a handful of well-known cultivars.

In 2008, Jurg Gertsch and colleagues published a paper in the Proceedings of the National Academy of Sciences titled Beta-caryophyllene is a dietary cannabinoid. They showed it is a selective full agonist at the CB2 receptor.

That is a strong result and it stands. Beta-caryophyllene binds CB2 the way a cannabinoid does, it is present in ordinary food, and it is on the FDA's list of substances generally recognized as safe as a food additive. It does not bind CB1, so it is not intoxicating.

This is the clearest case of a terpene doing something at a cannabinoid receptor, and it is worth separating from the vaguer terpene claims, because it rests on direct binding data rather than inference from smell and folklore.

The first is that cannabis with more than 0.5% myrcene is an indica and less than 0.5% is a sativa. This number circulates through hundreds of dispensary blogs and terpene guides. It traces back to no primary study. Nobody who repeats it cites the research, because there is none to cite. The indica and sativa split itself correlates poorly with chemical composition, which is why chemists prefer chemovar classification based on measured cannabinoid and terpene content.

The second is the terpene boiling point chart, which tells you to vape at 168 degrees Celsius for myrcene and 177 for limonene to selectively capture each one. The boiling points are real published values for pure compounds at standard pressure. Applying them to a vaporiser is not, because the temperature you set is not the temperature at the material, terpenes evaporate across a range well below their boiling points, and everything in a plant matrix behaves differently than an isolated compound in a flask. The chart is a plausible-looking extrapolation that has been repeated until it reads as established.

Both claims get repeated by people selling something. That is the useful signal.

Ethan Russo's 2011 paper in the British Journal of Pharmacology, Taming THC, is the most cited case for terpene and cannabinoid synergy. It is a careful review that proposes mechanisms and identifies where the evidence is thin, and it is worth reading rather than citing secondhand.

What it supports is that terpenes are pharmacologically active, that several have plausible mechanisms relevant to cannabinoid effects, and that synergy is worth investigating. What it does not do is establish that a given terpene profile produces a given experience in a given person. Russo says so himself.

Terpene content is a real and measurable property of a product, and a reason to prefer a full-spectrum extract that preserved them over one that did not. Precise predictions from a terpene percentage are not supported.

Most CBD products do not publish a terpene panel. Cannabinoid potency panels are standard; terpene panels cost extra and are usually only run by producers who consider the profile a selling point.

If a brand publishes one, it will list each terpene as a percentage of total weight, with the total terpene content summed. Anything above 1% total is a meaningfully terpene-rich extract. If a product markets a terpene profile and does not publish the panel, that is a question worth asking before buying.