THC, short for delta-9-tetrahydrocannabinol, is the main psychoactive compound in cannabis. It is the part that gets you high. It attaches to cannabinoid receptors in the brain and nervous system, which is why one molecule can shift mood, appetite, perception, and your sense of time. Below is how it works, how long it lasts, how dosing changes by method, and where the real risks sit.

How THC works in the body

Delta-9 THC binds CB1 receptors, which are packed into brain regions tied to memory, coordination, reward, and pain signaling. It also touches CB2 receptors, found mostly in immune tissue. That wide reach explains why the same compound can relax muscles, trigger hunger, blur short-term memory, and make a song hit harder, all within an hour.

THC is fat-soluble. It clears the bloodstream within hours but stores in fat tissue, which is one reason heavy users can test positive for weeks after they stop.

THC versus THCA

Raw cannabis holds little THC. It holds THCA, the acid form, and THCA does not get you high. Heat changes that. Smoking, vaping, baking, or decarboxylating flower in an oven converts THCA into THC. That matters when you read a label. A jar can list 25% total THC while the raw THCA number reads differently. Lab reports usually show both, plus the total after conversion.

Other cannabinoids ride along: CBD, CBG, CBN, and hemp-derived relatives like delta-8 THC, delta-10, THCV, and THCP. Delta-8 tends to feel weaker per milligram and shows up in gummies and vape cartridges. THCP has a longer molecular chain and may bind more strongly, though human data is thin.

How long THC lasts

  • Inhaled (flower, vape, concentrate): felt in 1 to 5 minutes, peak around 15 to 30 minutes, mostly gone in 1 to 3 hours.
  • Oral (edibles, drinks, capsules): 30 to 90 minutes before you feel anything, peak at 2 to 4 hours, and it can run 6 hours or longer.
  • Tinctures held under the tongue: faster than edibles, slower than smoke, about 15 to 45 minutes.
  • Topicals: no meaningful psychoactivity for most people. They act where you apply them.

The edible delay catches people. Eating more at minute 40 because nothing has happened yet is the most common route to a rough night.

Dosing in milligrams

In legal markets, 10 mg is the standard single edible dose, and many packages are scored into 5 mg or 2.5 mg pieces. Beginners do better at 2.5 to 5 mg. Inhaled THC is harder to measure, so start with one or two puffs and wait 15 minutes before deciding you need more. Concentrates run far stronger than flower, sometimes 70% THC or higher, and a single dab can deliver more than a full edible.

Legal status in the U.S.

Federally, delta-9 THC remains a Schedule I controlled substance under the Controlled Substances Act. The 2018 Farm Bill removed hemp, defined as cannabis with no more than 0.3% delta-9 THC by dry weight, from that definition, which opened the door to hemp-derived THC products in many states. State law is the layer that matters day to day. Recreational sales are legal in a growing list of states, medical-only in others, and a few still prohibit all forms. Recreational states enforce a 21 and over age rule.

Side effects and risks worth knowing

  • Short term: dry mouth, red eyes, faster heart rate, dizziness, anxiety or paranoia, and impaired coordination and memory.
  • Higher-risk patterns: heavy daily use, high-potency concentrates, and starting young.
  • Driving: THC slows reaction time and lane tracking. Wait until impairment fades, not just until you feel normal.
  • Cannabinoid hyperemesis syndrome: repeated severe vomiting in long-term heavy users, sometimes eased by hot showers. It needs medical care.
  • Pregnancy and adolescence: avoid. Brain development continues into the mid-20s.

Tolerance, dependence, and drug testing

Daily use builds tolerance within a couple of weeks. You need more to feel the same, and stopping can bring irritability, trouble sleeping, low appetite, and cravings. Those withdrawal symptoms are mild next to opioids but they are real. Standard urine tests look for THC-COOH metabolites. A single use might clear in a few days. Chronic heavy use can take a month or longer.

Buying THC products without guessing

I look for a batch number and a current lab report, then check total THC per package rather than per serving. That number is what tells you how the evening goes. Store edibles away from kids and pets, keep them in the original child-resistant packaging, and write the dose on the box if you split a gummy. If you are new to THC or coming back after a long break, buy a low-dose package first. You can always take more. You cannot take less.