When you smoke weed, THC passes from your lungs into your bloodstream within seconds, reaches your brain, and triggers a cascade of effects: your heart speeds up, your mood shifts, your short-term memory dulls, and your perception of time stretches. The full experience typically lasts 3 to 10 hours depending on how much you consume, how you consume it, and how often you use cannabis.
How THC Works in Your Brain
THC, the main psychoactive compound in cannabis, locks onto specific receptors in your brain called CB1 receptors. These receptors are part of a signaling system your body already uses to regulate mood, appetite, pain, and memory. THC essentially mimics the natural chemicals your brain produces for this system, but it activates these receptors far more intensely than your body normally would.
One of the most important things THC does is trigger a surge of dopamine in the brain’s reward center, a structure called the nucleus accumbens. This is the same mechanism behind the pleasurable effects of every known drug of abuse. THC binds to receptors in a region of the midbrain that normally keeps dopamine release in check. By quieting those brakes, it lets dopamine flood the reward pathway. That dopamine surge is what produces the euphoria, relaxation, and heightened sensory experience most people associate with being high.
What the High Feels Like
The effects of smoking cannabis start within minutes. Most people notice a wave of relaxation, mild euphoria, and altered sensory perception. Colors might seem more vivid, music more immersive, food more flavorful. Time often feels like it’s slowing down. Some people become talkative and giggly, while others turn quiet and introspective.
Not everyone has a pleasant experience. Cannabis can also cause anxiety, paranoia, or a sense of unease, particularly at higher doses or in people who are newer to it. Some users report feeling disoriented or detached from their surroundings. These negative effects are more common with today’s products, which are dramatically stronger than what was available a generation ago. Cannabis flower in the 1990s averaged about 5% THC. In 2022, the average was 21%, with some strains reaching 35%. Concentrates average 69% THC.
How Long the Effects Last
When you inhale cannabis smoke or vapor, THC enters your bloodstream through your lungs almost immediately. You’ll typically feel the peak effects within 15 to 30 minutes. From there, a meta-analysis of existing research identified a “window of impairment” lasting roughly 3 to 10 hours after use. Several factors determine where you fall in that range.
Higher doses produce longer-lasting effects. Edibles last significantly longer than smoking because THC is absorbed through the digestive system more slowly. And if you use cannabis only occasionally, you’ll generally feel more impaired and for a longer duration than someone who uses it regularly. Regular users develop a tolerance that blunts both the intensity and the length of the high.
Immediate Physical Effects
Your body responds to cannabis almost as quickly as your brain does. Heart rate increases and blood pressure rises immediately after use, according to the CDC. For most young, healthy people this is a temporary and harmless spike. But for people with existing heart conditions, this cardiovascular stress may increase the risk of stroke or heart attack. Most of the research linking cannabis to serious cardiovascular events involves smoked cannabis specifically.
Other common physical effects include dry mouth, red eyes, increased appetite (the well-known “munchies”), and slowed reaction time. Some people experience dizziness or mild nausea, especially with higher doses.
What It Does to Your Thinking
Cannabis causes measurable cognitive impairment while you’re high, and the effects are not evenly distributed across mental abilities. A meta-analysis of more than 52 studies found that verbal learning and memory take the biggest hit. Your ability to encode new information, hold it in mind, and retrieve it later drops substantially. This is why people who are high frequently lose their train of thought mid-sentence or forget what they were about to do.
Processing speed and executive function (your ability to plan, organize, and switch between tasks) also decline, though to a more moderate degree. Attention and impulse control are mildly affected. All of these effects follow a dose-response pattern: the more THC you consume, the worse the impairment. Reaction times slow in a dose-dependent way as well, which is a key reason cannabis-impaired driving is dangerous.
What Smoking Does to Your Lungs
Cannabis smoke contains many of the same toxins, irritants, and carcinogens found in tobacco smoke. Regardless of whether you use a joint, pipe, or bong, inhaling combusted plant material can scar lung tissue and damage small blood vessels. Regular smoking leads to higher rates of bronchitis, chronic cough, and excess mucus production. The good news is that these respiratory symptoms generally improve after people stop smoking cannabis.
This is one reason some users switch to vaporizers, which heat cannabis below the point of combustion. While vaping reduces exposure to some combustion byproducts, it is not risk-free and the long-term effects are still being studied.
Mental Health Risks With Regular Use
One of the most consistent findings in cannabis research is the link between regular use and psychotic symptoms. A landmark study of over 50,000 Swedish military conscripts found that those who had tried cannabis by age 18 were 2.4 times more likely to later be diagnosed with schizophrenia. The risk increased with frequency of use, a dose-response pattern that has been replicated in studies from the Netherlands, Germany, and New Zealand.
This doesn’t mean smoking weed once will cause psychosis. The elevated risk primarily applies to regular, heavy use, and it’s higher in people who start young or who have a pre-existing vulnerability to psychotic disorders. A French study of college students found that during time periods when cannabis was used, all users reported more unusual perceptions, but students who were already identified as vulnerable to psychosis experienced significantly more strange impressions and perceptual distortions. In other words, cannabis appears to amplify a vulnerability that may already be present.
Dependence and Withdrawal
Cannabis can be addictive. While the risk of dependence is lower than with alcohol, nicotine, or opioids, heavy long-term users can develop a recognized withdrawal syndrome when they stop. Symptoms typically begin within a few days of quitting and include irritability, anxiety, insomnia, decreased appetite, restlessness, and depressed mood. Physical symptoms like stomach pain, sweating, chills, headaches, and tremors can also occur.
To qualify as clinical withdrawal, a person needs to experience at least three of these symptoms after stopping heavy, prolonged use, and the symptoms need to meaningfully interfere with daily life. For many people, withdrawal is uncomfortable but manageable, peaking in the first week and fading over the following one to two weeks. But for heavy daily users, the irritability and sleep disruption can be significant enough to drive relapse.
How Tolerance Builds
With repeated exposure, your brain adapts to the constant presence of THC. CB1 receptors become less responsive, and some are pulled from the cell surface entirely. This is why regular users need more cannabis to achieve the same effect and why they experience less cognitive impairment at the same dose compared to occasional users. These neuroadaptations affect not just the reward system but also downstream circuits involved in motivation, learning, and habit formation. When cannabis use stops, the brain gradually recalibrates, but this process takes time, which is partly why withdrawal symptoms emerge in heavy users.