What cannabis actually is
Cannabis is a flowering plant in the Cannabaceae family. It makes more than 100 distinct compounds called cannabinoids, along with dozens of aromatic compounds called terpenes. What sits in a dispensary jar is one particular variety, bred over decades toward a particular ratio of those compounds, much as a Cabernet Sauvignon grape is one particular variety of Vitis vinifera bred toward a particular wine.
The two cannabinoids most people can name are THC (tetrahydrocannabinol) and CBD (cannabidiol), and they behave very differently. THC is the compound behind the feeling of being high. CBD is not intoxicating on its own, but it changes how the body responds to THC and has direct effects of its own on pain, anxiety, and seizure thresholds.
Everything else on a label matters, but in smaller ways: minor cannabinoids such as CBG, CBN, and CBC, and terpenes such as myrcene, limonene, pinene, and caryophyllene. Understand THC and CBD and you understand roughly 80 percent of what counts.
The endocannabinoid system, in about 400 words
The body already makes cannabinoids of its own. They are called endocannabinoids (endo for endogenous, meaning made inside you), and they help regulate sleep, mood, appetite, pain signalling, immune response, and a half-dozen other things that need to stay in balance.
They act on two main receptor types, CB1 and CB2. CB1 receptors cluster in the brain and nervous system, which is why THC feels the way it does. CB2 receptors cluster in immune tissue, which is why cannabis can have anti-inflammatory effects that do not depend on feeling high.
When a person uses cannabis, the plant's cannabinoids dock onto the same receptors the body's own cannabinoids use. THC fits well into CB1. CBD works less directly: it does not bind strongly at CB1 or CB2, but it changes how those receptors respond to the cannabinoids around them, and it shifts the enzymes that break cannabinoids down.
That is the 90 percent version. The 10 percent that pharmacists care about is that every person has a slightly different baseline: how many CB1 receptors they have, how quickly their enzymes clear cannabinoids, how sensitive their nervous system is to small shifts. That is why two people can take the same dose and have genuinely different experiences. It is not weakness and it is not tolerance. It is biochemistry.
THC and CBD: the minimum you need
THC is the intoxicating compound. It relieves pain, reduces nausea, stimulates appetite, and produces the altered thinking most people call being high. Its dose-response curve is biphasic: small amounts often reduce anxiety, while larger amounts can increase it. This is why more is frequently worse rather than better.
CBD is not intoxicating. It reduces anxiety, works as an anticonvulsant (it is the active ingredient in Epidiolex, the FDA-approved seizure medicine), and has anti-inflammatory effects. It also changes how THC feels: products with a balanced CBD-to-THC ratio are usually gentler than pure-THC products at the same dose.
A useful picture: if THC is the accelerator, CBD is the governor. Products that pair the two tend to be more predictable. Products that are close to pure THC can produce the strongest effects and also the strongest side effects, including mental fog, a racing heart, and paranoia, especially in patients who are new to cannabis.
Terpenes, the part the industry oversells
Terpenes are aromatic compounds. They are the reason one strain smells of pine and another of citrus. Almost every plant on Earth makes them; cannabis is not special in that respect.
What makes them useful in cannabis is that they subtly shape how the cannabinoids feel. Myrcene tends toward sedating, limonene toward uplifting, caryophyllene toward anti-inflammatory. Those effects are real but small next to the THC and CBD content. A budtender who says a particular terpene profile will treat a particular condition is overselling; the research does not support claims that strong.
Tiffany's rule of thumb: use terpene dominance as a tiebreaker between two products with similar cannabinoid profiles, never as the main reason to pick a product.
A short honest history
Cannabis has been used as medicine for at least two thousand years. It appears in the Chinese pharmacopoeia Shen Nong Ben Cao Jing, in the writings of Ibn al-Baytar, in the formularies of medieval Islamic medicine, and in the United States Pharmacopoeia from 1851 to 1942.
It left the USP not because its medical uses had been disproven but because of the 1937 Marihuana Tax Act, a law written against the medical cannabis tradition and in favour of the pharmaceutical industry of the day. From 1942 until roughly the 1990s, cannabis sat effectively outside medicine in the United States.
What is happening now is a return, not an invention. The difference is that a patient in 2026 has tools that did not exist in 1851: standardized cannabinoid content on labels, third-party lab testing, published pharmacokinetic research, and the ability to check interactions against every prescription they take. The plant is not new. The infrastructure around it is.
Before your first dispensary visit
If only four things stick from this lesson, make them these: cannabis works through a receptor system the body already uses; THC is intoxicating and CBD is not, and they behave differently; individual variation in dosing is real, so start low; and everything else is fine tuning.
The next lesson is How to read a label. Once you know what the cannabinoids do, a label stops being a wall of numbers and turns into a recipe you can read.