How does marijuana affect the brain? You really need to know this.

Don’t kid yourself, Marijuana has both short-and long-term effects on the brain.

Image of a cross section of the brain with marked areas that are affected by THC.THC acts on numerous areas in the brain (in yellow).

Short-Term Effects

When a person smokes marijuana, THC quickly passes from the lungs into the bloodstream. The blood carries the chemical to the brain and other organs throughout the body. The body absorbs THC more slowly when the person eats or drinks it. In that case, they generally feel the effects after 30 minutes to 1 hour.

THC acts on specific brain cell receptors that ordinarily react to natural THC-like chemicals. These natural chemicals play a role in normal brain development and function.

Marijuana overactivates parts of the brain that contain the highest number of these receptors. This causes the “high” that people feel. Other effects include:

  • altered senses (for example, seeing brighter colors)
  • altered sense of time
  • changes in mood
  • impaired body movement
  • difficulty with thinking and problem-solving
  • impaired memory
  • hallucinations (when taken in high doses)
  • delusions (when taken in high doses)
  • psychosis (when taken in high doses)

Long-Term Effects

Marijuana also affects brain development. When people begin using marijuana as teenagers, the drug may impair thinking, memory, and learning functions and affect how the brain builds connections between the areas necessary for these functions. Researchers are still studying how long marijuana’s effects last and whether some changes may be permanent.

For example, a study from New Zealand conducted in part by researchers at Duke University showed that people who started smoking marijuana heavily in their teens and had an ongoing marijuana use disorder lost an average of  IQ points between ages 13 and 38. The lost mental abilities didn’t fully return in those who quit marijuana as adults. Those who started smoking marijuana as adults didn’t show notable IQ declines.

In another recent study on twins, those who used marijuana showed a significant decline in general knowledge and in verbal ability (equivalent to 4 IQ points) between the preteen years and early adulthood, but no predictable difference was found between twins when one used marijuana and the other didn’t. This suggests that the IQ decline in marijuana users may be caused by something other than marijuana, such as shared familial factors (e.g., genetics, family environment).  NIDA’s Adolescent Brain Cognitive Development (ABCD) study, a major longitudinal study, is tracking a large sample of young Americans from late childhood to early adulthood to help clarify how and to what extent marijuana and other substances, alone and in combination, affect adolescent brain development. Read more about the ABCD study on our Longitudinal Study of Adolescent Brain and Cognitive Development.

What are the other health effects of marijuana?

Marijuana use may have a wide range of effects, both physical and mental.

Physical Effects

  • Breathing problems. Marijuana smoke irritates the lungs, and people who smoke marijuana frequently can have the same breathing problems as those who smoke tobacco. These problems include daily cough and phlegm, more frequent lung illness, and a higher risk of lung infections. Researchers so far haven’t found a higher risk for lung cancer in people who smoke marijuana.
  • 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. One study found that about 20% of pregnant women 24-years-old and younger screened positive for marijuana. However, this study also found that women were about twice as likely to screen positive for marijuana use via a drug test than they state in self-reported measures.  This suggests that self-reported rates of marijuana use in pregnant females is not an accurate measure of marijuana use and may be under-reporting their use. Additionally, in one study of dispensaries, non-medical personnel at marijuana dispensaries were recommending marijuana to pregnant women for nausea, but medical experts warn against it. This concerns medical experts because marijuana use during pregnancy is linked to lower birth weight and 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. Children exposed to marijuana in the womb have an increased risk of problems with attention, memory, and problem-solving compared to unexposed children.  Some research also suggests that moderate amounts of THC are excreted into the breast milk of nursing mothers. With regular use, THC can reach amounts in breast milk that could affect the baby’s developing brain. More research is needed. Read our Marijuana Research Report for more information about marijuana and pregnancy.
  • Intense Nausea and Vomiting. Regular, long-term marijuana use can lead to some people to develop Cannabinoid Hyperemesis Syndrome. This causes users to experience regular cycles of severe nausea, vomiting, and dehydration, sometimes requiring emergency medical attention.
Silhouette of a seated young male, hunched over with his head resting in his hand.

Mental Effects

Long-term marijuana use has been linked to mental illness in some people, such as:

  • temporary hallucinations
  • temporary paranoia
  • 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.

The above article in its original form can be found HERE.


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