How does marijuana affect the brain? (吸大麻怎样影响人的大脑?)
Marijuana has both short- and long-term effects on the brain. (吸大麻对大脑既有短期的影响也有长期的影响)

THC acts on numerous areas in the brain (in yellow).
Image by NIDA
Short-Term Effects (短期影响)
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, he or she generally feels 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
Long-Term Effects (长期影响)
Marijuana also affects brain development. When people begin using marijuana 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 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 8 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.
3 However, recent results from two studies on twins didn't support a causal relationship between marijuana use and IQ loss. Those who used marijuana did show a significant decline in verbal ability (equivalent to 4 IQ points) and in general knowledge between the preteen years and early adulthood. However, no predictable difference was found between twins when one used marijuana and one didn't. This suggests that the IQ decline may be caused by shared familial factors (e.g., genetics, family environment), and not by marijuana use itself.
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