Marijuana affects brain development. When marijuana users begin using as teenagers, the drug may reduce thinking, memory, and learning functions and affect how the brain builds connections between the areas necessary for these functions.
Marijuana’s effects on these abilities may last a long time or even be permanent.
For example, a study showed that people who started smoking marijuana heavily in their teens and had an ongoing cannabis use disorder lost an average of eight IQ points between ages 13 and 38. The lost mental abilities did not fully return in those who quit marijuana as adults. Those who started smoking marijuana as adults did not show notable IQ declines.
Marijuana use may have a wide range of effects, both physical and mental.
Physical effects
- Breathing problems. Marijuana smoke irritates the lungs, and frequent marijuana smokers can have the same breathing problems that tobacco smokers have. These problems include daily cough and phlegm, more frequent lung illness, and a higher risk of lung infections. Researchers still do not know whether marijuana smokers have a higher risk for lung cancer.
- Increased heart rate. Marijuana raises heart rate for up to 3 hours after smoking. This effect may increase the chance of heart attack. Older people and those with heart problems may be at higher risk
- Problems with child development during and after pregnancy. Marijuana use during pregnancy is linked to increased risk of both brain and behavioral problems in babies. If a pregnant woman uses marijuana, the drug may affect certain developing parts of the fetus’s brain. Resulting challenges for the child may include problems with attention, memory, and problem-solving. Additionally, some research suggests that moderate amounts of THC are excreted into the breast milk of nursing mothers. The effects on a baby’s developing brain are still unknown.
Long-term marijuana use has been linked to mental illness in some users, such as:
- temporary hallucinations—sensations and images that seem real though they are not
- temporary paranoia—extreme and unreasonable distrust of others
- worsening symptoms in patients with schizophrenia (a severe mental disorder with symptoms such as hallucinations, paranoia, and disorganized thinking)
Marijuana use has also been linked to other mental health problems, such as depression, anxiety, and suicidal thoughts among teens. However, study findings have been mixed.
Compared to nonusers, heavy marijuana users more often report the following:
- lower life satisfaction
- poorer mental health
- poorer physical health
- more relationship problems
Users also report less academic and career success. For example, marijuana use is linked to a higher likelihood of dropping out of school. It is also linked to more job absences, accidents, and injuries.
Marijuana