Cannabis contains more than 550 distinct chemical compounds, including over 100 cannabinoids, dozens of aromatic terpenes, and a handful of flavonoids found nowhere else in nature. The two compounds most people have heard of, THC and CBD, are just the headliners. The full chemical profile of the plant is far more complex, and each class of compound plays a different role in how cannabis smells, tastes, and affects your body.
THC: The Compound That Gets You High
Delta-9-tetrahydrocannabinol, or THC, is the primary psychoactive ingredient in cannabis. It works by activating a receptor in your brain called CB1, which adjusts how nerve cells communicate. When THC binds to this receptor, it reduces the release of several chemical messengers between neurons. That disruption is what produces the high: altered perception, euphoria, relaxation, slowed reaction time, and increased appetite.
THC also interacts with pain-signaling pathways through at least three different receptor types, which is why cannabis has a long history of use for pain relief. Beyond the brain, THC affects receptors throughout the body, including in the immune system, gut, and spinal cord.
The concentration of THC in cannabis has risen dramatically. Samples seized by the DEA averaged about 4% THC in 1995. By 2022, that average had climbed to roughly 16%. Today’s flower commonly sits around 20%, and concentrated extracts can reach 75 to 80%. That shift matters because higher-potency products deliver more THC per use, which changes both the intensity and the risk profile.
CBD: THC’s Non-Intoxicating Counterpart
Cannabidiol, or CBD, does not produce a high. It actually works against THC at the CB1 receptor, acting as a kind of dimmer switch that can blunt some of THC’s more intense effects. This is one reason strains with a higher CBD-to-THC ratio tend to feel less overwhelming.
CBD has its own set of biological activities. It boosts levels of adenosine, a naturally calming molecule, by blocking the transporter that normally clears it away. It also activates a pain- and temperature-sensing channel called TRPV1, which may explain why CBD shows up in research on anxiety and inflammation. In animal studies, this channel activation produces both pain relief and anxiety reduction. CBD’s anti-seizure properties led to the first cannabis-derived prescription drug approved in the United States.
Minor Cannabinoids
Beyond THC and CBD, the plant produces over 120 additional cannabinoids in smaller quantities. All of them trace back to a single parent molecule called CBGA, which the plant converts into different end products through separate enzyme pathways. A few of the better-known minor cannabinoids include:
- CBG (cannabigerol): The direct descendant of that parent molecule. It’s present in larger amounts in young plants before the enzymes convert it into THC, CBD, or other cannabinoids.
- CBN (cannabinol): Forms when THC degrades over time through exposure to heat, light, or oxygen. Old cannabis tends to have more CBN.
- CBC (cannabichromene): One of the more abundant minor cannabinoids, produced through its own enzyme branch.
These minor cannabinoids interact with many of the same receptors as THC and CBD, plus additional targets in the serotonin and pain-sensing systems. Early clinical reports suggest potential benefits for neuropathic pain, skin conditions, and neurodegenerative diseases, though research is still limited compared to what we know about THC and CBD.
Terpenes: Where the Smell Comes From
The pungent, instantly recognizable smell of cannabis comes largely from terpenes, the same class of aromatic compounds found in pine trees, citrus peels, and black pepper. Cannabis produces dozens of terpenes, and the specific blend determines whether a given strain smells earthy, fruity, or diesel-like. The three most common are:
- Myrcene: The most abundant terpene in most strains. It has a musky, hop-like scent and may enhance pain relief by triggering the release of the body’s own opioid-like molecules. Strains high in myrcene (above 0.5% of total weight) are associated with heavier, more sedating effects.
- Limonene: Carries a citrus aroma. It raises serotonin and dopamine levels, which may contribute to mood-lifting and anti-anxiety effects.
- Beta-caryophyllene: Smells like black pepper and is the most abundant sesquiterpene in cannabis, especially after heating. Uniquely, it directly activates the CB2 receptor in the immune system without any psychoactive effect, giving it anti-inflammatory properties.
Terpenes are part of the reason two strains with similar THC percentages can feel quite different. The idea that terpenes and cannabinoids work together to shape the overall experience is sometimes called the “entourage effect,” though the science behind that concept is still being worked out.
What Gives Cannabis Its Skunky Smell
Terpenes account for most of the plant’s aroma, but they don’t explain the distinctly skunky, gassy smell of certain strains. That comes from a separate family of prenylated volatile sulfur compounds. These sulfur molecules, including prenylthiol and prenylmethyl sulfide, produce the sharp, pungent notes people associate with potent cannabis. They exist in tiny concentrations but have an outsized effect on smell because the human nose is extremely sensitive to sulfur.
Flavonoids Unique to Cannabis
Cannabis produces about 20 flavonoids, the same class of plant pigments found in berries, tea, and citrus. Three of them, Cannflavin A, B, and C, exist only in cannabis. In lab studies using human rheumatoid cells, Cannflavins A and B were roughly 30 times more potent than aspirin at reducing a key inflammatory signal. They achieve this through a different mechanism than common anti-inflammatory drugs, which means they may avoid the stomach irritation those drugs can cause. Cannflavins are present in small amounts in the plant, but their potency has generated interest in isolating them for medical use.
Where These Compounds Are Made
Nearly all of the cannabinoids, terpenes, and flavonoids are produced and stored in tiny mushroom-shaped structures called glandular trichomes. These are the frosty, crystal-like bumps visible on cannabis flowers. Each trichome has a stalk topped by a bulbous head containing a ring of secretory cells, anywhere from 8 to 16 depending on the trichome type. These cells synthesize cannabinoids and terpenes through a multi-step process that starts in the cell interior and finishes in a storage cavity beneath the trichome’s outer skin. When you grind or handle cannabis and your fingers get sticky, that residue is trichome resin.
Hemp vs. Marijuana: Same Plant, Different Chemistry
Hemp and marijuana are both Cannabis sativa. The only formal distinction is legal, not botanical: in the United States, cannabis containing 0.3% THC or less by dry weight is classified as hemp. Anything above that threshold is marijuana. Hemp plants tend to be higher in CBD and lower in THC, while marijuana cultivars have been selectively bred for maximum THC production. The non-cannabinoid compounds, terpenes, flavonoids, and other molecules, overlap substantially between the two.
Contaminants in Untested Cannabis
What’s in weed isn’t always limited to what the plant produces naturally. Cannabis that hasn’t been lab-tested can carry a range of contaminants. In one analysis of legalized products in Washington State, nearly 85% of samples contained significant levels of pesticides, including known carcinogens, endocrine disruptors, and neurotoxins. The pesticides spanned insecticides, fungicides, and herbicides.
Heavy metals are another concern. Cannabis is an effective bioaccumulator, meaning it readily absorbs metals like arsenic, cadmium, lead, and mercury from soil and water. There have been documented cases of lead poisoning from cannabis that was deliberately adulterated to increase its weight for sale.
Fungal contamination is common when cannabis is harvested wet or stored in humid conditions. Researchers have found multiple species of Aspergillus and Penicillium on cannabis samples. Some Aspergillus strains produce aflatoxins, which are potent carcinogens, and these have been detected in both raw cannabis and its smoke. This is one of the stronger arguments for buying from regulated markets where lab testing is required.