Long-term marijuana use affects the brain, lungs, heart, and mental health, with the severity depending on how often you use, how early you started, and the potency of the product. Today’s marijuana is far stronger than it used to be: the average THC concentration in seized samples rose from about 4% in 1995 to over 16% in 2022, meaning the long-term risks studied in earlier decades may underestimate what current users face.
Memory, Attention, and IQ
The cognitive effects of chronic marijuana use are among the best-documented long-term consequences. Verbal memory takes the biggest hit. Chronic users learn and recall fewer words on standardized tests, showing deficits in encoding, storing, and retrieving information. Working memory, the mental scratchpad you use to hold and manipulate information in real time, is also impaired across both visual and auditory tasks.
Chronic users are also more prone to false memories, recalling events that didn’t happen or accepting incorrect information as true. In one study, regular users were more likely to endorse false details even after a prolonged period of abstinence, suggesting the effect isn’t simply about being high at the time.
Processing speed slows in a dose-dependent way: the more THC consumed, the slower the reaction times and the worse the motor coordination, with subtle alterations persisting even after the acute effects wear off. Sustained and alternating attention also suffer, with long-term users performing worse than short-term users, who in turn performed worse than non-users. One longitudinal study found that chronic users lost an average of about 4 IQ points from childhood to adulthood, a modest but measurable decline.
Effects on the Teenage Brain
The adolescent brain is especially vulnerable because it’s still under construction. In a study tracking 799 teenagers over five years with brain imaging, cannabis use was linked to accelerated thinning of the prefrontal cortex, the region responsible for decision-making, impulse control, and planning. Teens who used more cannabis had thinner prefrontal cortices than those who used less, and the thinning was greatest in areas that naturally thin the most during normal development, essentially speeding up a process that’s supposed to happen gradually.
The thinning was concentrated in brain areas with high densities of cannabinoid receptors, the docking sites where THC acts. At the five-year follow-up, this cortical thinning was significantly associated with greater attentional impulsiveness, meaning the structural changes translated into measurable behavioral differences. This is one reason the risk of developing a problematic relationship with cannabis is higher for people who begin using before age 18.
Mental Health and Psychosis Risk
Any cannabis use is associated with a 40% increased risk of psychosis. Daily use pushes that risk to two to three times higher than non-users. Higher-potency products are linked to both a greater likelihood of psychotic symptoms and an earlier age of onset. These associations hold up across multiple large studies, though individual risk varies based on genetics and other factors.
The relationship between cannabis and schizophrenia is not simply that people predisposed to psychosis happen to use more cannabis. While that’s part of the picture, the dose-dependent pattern (more use equals more risk) and the potency effect (stronger products, higher risk) both point toward a causal contribution, particularly in people with genetic vulnerability.
Lung and Respiratory Damage
Smoked cannabis, regardless of the device used, harms lung tissue. It causes scarring and damages small blood vessels in the lungs. Chronic smokers face a higher risk of bronchitis, persistent cough, and excess mucus production. The good news is that these symptoms generally improve after quitting.
The connection to lung cancer, emphysema, and COPD is less clear. Cannabis smoke contains many of the same toxins and carcinogens as tobacco smoke, but the research hasn’t yet established definitive long-term risk numbers for these diseases. This gap exists partly because most long-term cannabis smokers also smoke or have smoked tobacco, making it hard to isolate the effects.
Heart and Stroke Risk
Daily cannabis use is associated with a 25% increased risk of heart attack and a 42% increased risk of stroke compared to non-use. These numbers come from a large study of U.S. adults published in the Journal of the American Heart Association.
The most striking finding involved people who had never smoked tobacco or used e-cigarettes. In that group, daily cannabis use was associated with more than double the risk of stroke. This matters because it removes tobacco as a confounding factor, suggesting cannabis itself contributes to cardiovascular risk rather than simply being a marker for people who also smoke cigarettes. The mechanisms likely involve the effects of THC on heart rate, blood pressure, and blood vessel function.
Cannabis Use Disorder and Dependence
Roughly 3 in 10 people who use cannabis develop cannabis use disorder, characterized by difficulty controlling use, continued use despite negative consequences, and withdrawal symptoms when stopping. Starting before age 18 significantly increases this risk.
Withdrawal is real and can be uncomfortable. Symptoms typically begin within 24 to 48 hours of stopping heavy, long-term use and peak around day three. The most common symptoms include irritability, anxiety, restlessness, decreased appetite, depressed mood, insomnia, and vivid or disturbing dreams. Most symptoms resolve within two weeks, though some can linger for three weeks or longer in very heavy users.
Cannabinoid Hyperemesis Syndrome
Cannabinoid hyperemesis syndrome (CHS) is a condition that develops in long-term users, typically after about 10 to 12 years of regular use. It causes cycles of severe nausea, intense abdominal pain, and repeated vomiting that can reach up to five times per hour. A hallmark feature is that hot showers provide temporary relief, and many people with CHS shower compulsively for hours each day.
CHS often begins with a prodromal phase of morning nausea and stomach discomfort that can last months or even years before progressing to full episodes. The only proven treatment is stopping cannabis use entirely. People who resume use after recovery typically see the symptoms return.
Pregnancy and Prenatal Exposure
Cannabis use during pregnancy may affect the developing brain of the fetus. Studies suggest that children exposed to cannabis in utero are more likely to have problems with attention, memory, problem-solving, and behavior later in life. The research in this area is still growing, but the existing evidence is consistent enough that prenatal exposure is considered a meaningful risk factor for neurodevelopmental differences in children.