How does cannabis affect the brain?
Cannabis contains more than 100 compounds called cannabinoids. The two studied most are delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC causes the high. It binds to cannabinoid receptors on neurons and changes how those cells send signals. The body makes its own cannabinoids, such as anandamide, that use the same receptors. THC takes over that system.
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THC and the CB1 receptor
CB1 receptors sit on neurons in the brain and spinal cord. THC binds to CB1 as a partial agonist. That binding lowers the release of other neurotransmitters, including dopamine, GABA, and glutamate. CB1 receptors cluster in the cerebral cortex, hippocampus, cerebellum, basal ganglia, and amygdala.
CBD has low affinity for CB1. It does not produce the same high. Research ties CBD to other targets, such as the serotonin receptor 5-HT1A and the enzyme FAAH.
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Brain regions and what changes
- Hippocampus: forms new memories. THC disrupts short-term memory and the move to long-term storage.
- Cerebellum and basal ganglia: control movement and timing. THC slows reaction time and affects balance.
- Cerebral cortex: handles attention, reasoning, and decisions. THC changes all three.
- Amygdala: processes emotion. High THC doses can trigger anxiety or paranoia.
- Nucleus accumbens: reward. THC raises dopamine signaling here. That rise supports repeated use.
- Hypothalamus and brainstem: manage appetite, body temperature, and heart rate. THC shifts appetite and can raise heart rate by 20 to 50 beats per minute.
How fast effects start
Inhaled THC reaches the brain in 1 to 10 minutes. Peak effects arrive at 15 to 30 minutes and fade over 2 to 4 hours. Edibles and drinks absorb in 30 to 90 minutes. Peak effects arrive at 2 to 4 hours. Effects last 4 to 12 hours. THC stores in body fat. THC metabolites can be detected for days in light users and for weeks in heavy users.
Short-term effects on the brain
- Memory: trouble holding a new fact or a name.
- Attention: trouble tracking two tasks at once.
- Coordination: slower reaction time behind the wheel.
- Mood: calm at low doses, anxiety at high doses.
- Perception: time feels slower.
- Psychosis: paranoia, delusions, or hallucinations at very high doses. These effects stop when the drug clears.
Repeated use and tolerance
The brain adjusts to THC. Neurons reduce the number of CB1 receptors, so the same dose does less. This is tolerance. Stopping after heavy use can cause withdrawal: irritability, sleep problems, headaches, and appetite changes. Symptoms peak in the first week and ease over 2 to 4 weeks.
The National Institute on Drug Abuse reports that about 3 in 10 people who use cannabis meet criteria for cannabis use disorder at some point. Risk rises with daily use and with products that contain high THC.
Adolescent brain
The brain keeps building connections into the mid-20s. Cannabis use in the teen years is linked to problems with attention, memory, and learning. Starting young and using often raises the odds of cannabis use disorder and of anxiety or depression later. Researchers do not know how much of this reverses after a person stops.
What research does not settle
Studies do not agree on long-term memory effects after months of abstinence. Data on CBD and brain function come from small trials. High-THC products, concentrates, and vapes changed the market, and their long-term effects are not measured yet.