THC (delta-9-tetrahydrocannabinol) is the main psychoactive compound in cannabis. It binds to CB1 receptors in the brain and nervous system, which causes the high along with shifts in mood, appetite, memory, and pain perception.

Cannabis plants make more than 100 cannabinoids, but THC drives most of the effects people notice. Its concentration in commercial flower has climbed over the past few decades, so dose matters more now than it did in the past.

What does THC do in the body?

THC mimics anandamide, a neurotransmitter your body makes on its own. The compound locks onto CB1 receptors in the brain and CB2 receptors in the immune system, then triggers a release of dopamine. That dopamine surge explains the euphoria, the giggles, and the hunger.

Effects start within minutes when you smoke or vape. Swallowed THC takes longer because it passes through the liver first, where enzymes convert part of it into 11-hydroxy-THC, a metabolite that enters the brain with more force.

How long does THC stay in your system?

Blood levels of THC peak about 10 minutes after smoking and drop fast. The metabolites linger. One use can show on a urine test for a few days, while daily use can show for weeks. Body fat, hydration, and test sensitivity all change the window.

How potent is cannabis today?

Average THC content in US flower rose from under 2% in the early 1990s to about 15-25% at retail today, and concentrates can pass 80%. Exact numbers vary by lab and product, but the direction is clear: one joint today can carry several times the THC of one from 1990.

Potency labels are not perfect. Labs differ in method, and some products test higher than the label suggests. If you want a predictable dose, buy from a shop that publishes batch results.

THC vs CBD

  • THC binds CB1 receptors well and produces a high. CBD binds them poorly and does not.
  • CBD can blunt some THC effects, including anxiety and racing thoughts, when the two are taken together.
  • THC has therapeutic uses such as nausea and appetite support. CBD has an FDA-approved use for certain seizure disorders.

Common forms of THC

Legal markets sell THC in more forms than most people expect. The delivery method changes how fast you feel it and how long it lasts.

  • Flower: smoked or vaped; effects in minutes, lasting 1-3 hours.
  • Vape cartridges: fast onset, high potency, easy to overdo.
  • Edibles: 30-90 minute onset, effects lasting 4-8 hours.
  • Tinctures: held under the tongue; onset between edibles and smoke.
  • Concentrates: wax, shatter, rosin; 60-90% THC.
  • Capsules and drinks: measured doses, no smoke.

Why edibles hit harder

Your liver turns delta-9-THC into 11-hydroxy-THC, which is more potent and lasts longer. Because digestion is slow, people who take a second dose at 45 minutes often overshoot. Wait two hours before adding more.

Side effects and risks

Short-term effects include dry mouth, red eyes, fast heart rate, dizziness, and short-term memory trouble. Higher doses can bring paranoia, panic, and nausea. These pass, but they feel awful while they last.

Risks grow with regular use. Heavy use links to cannabis use disorder, worse anxiety in some people, and bronchitis from smoking. Cannabis smoke carries many of the same irritants as tobacco smoke, minus the nicotine.

Who should skip THC

  • Anyone under 21 (or 18 in medical programs where allowed)
  • People with a personal or family history of psychosis
  • Pregnant or breastfeeding people
  • Anyone taking blood thinners, sedatives, or certain seizure drugs

Is THC legal in the US?

Federal law still lists THC as a Schedule I controlled substance under the Controlled Substances Act, though hemp-derived THC with no more than 0.3% delta-9 by dry weight is legal under the 2018 Farm Bill. State rules split three ways: adult-use, medical-only, and prohibited.

More than 20 states allow adult use, and most allow medical cannabis. Crossing a state line with product, even between two legal states, breaks federal law. Check your state's rules before you buy or travel.

How to read a THC label

  • Total THC: delta-9 plus THCA after decarboxylation. This is the number that matters for dose.
  • Serving size: in legal markets, 10 mg is the standard single serving for edibles.
  • Batch date and lab: fresh product and a named testing lab are good signs.
  • Terpenes and minor cannabinoids: listed on better labels, useful for predicting flavor and effect.

THC FAQ

Can you overdose on THC?

No fatal overdose from cannabis alone has been confirmed. The dose that kills lab animals sits far above any amount a person could consume. You can still take too much and have a bad few hours.

Does THC help with sleep?

THC can shorten the time it takes to fall asleep, and many people use it for that reason. Tolerance builds fast, and stopping after months of daily use often brings vivid dreams and rough sleep for a week.

Will THC show on a drug test?

Yes. Standard urine tests screen for THC metabolites (carboxy-THC), which stay detectable for days after one use and weeks after daily use. CBD products may carry trace THC, and full-spectrum hemp can trigger a positive result in some cases.

What is delta-8 THC?

Delta-8 is a minor cannabinoid with a double bond in a different spot. It produces a milder high than delta-9 and sits in a legal gray zone for hemp-derived products. Rules differ by state.

Does THC expire?

THC degrades over time into CBN, which is far less psychoactive. Flower kept in a sealed jar away from light and heat holds potency for about a year. Edibles and tinctures keep longer with proper storage.

Buying THC at a dispensary

Start low and go slow. Take extra care with edibles and concentrates, since both hide their strength in a small package. Ask the budtender for the lab report if you want to check potency and contaminants.

Keep the packaging for dose info, and store everything away from kids and pets. If you take prescription drugs, tell your doctor that you use THC so they can watch for interactions.