Last updated: 25 May 2023 & medically reviewed by Hailey Shafir
Researchers are still finding out more about the long-term impacts of marijuana use on the brain. Early research suggests that marijuana use (especially in kids and teens) can have lasting negative impacts on the brain, including lower problem-solving, cognitive functioning, speed, and memory. Heavy and frequent users of marijuana may be at higher risk for these neurological effects, especially when they begin using young and continue for many years.
- Some studies suggest regular marijuana use in adolescence is associated with a reduced volume of specific brain regions involved in a broad range of executive functions such as memory, learning, and impulse control compared to people who do not use
- The study also showed that those who abused marijuana heavily in adolescence but quit in adulthood did not recover IQ points and those who only started using marijuana in adulthood lost no IQ points at all
- The toxic components of synthetic marijuana, or “fake weed”, can cause increased heart rate, vomiting, bleeding, and produces powerful mind-altering effects
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Can weed kill brain cells?
Medicinal and legal recreational marijuana use is becoming increasingly prevalent throughout the US, with more states legalizing the substance every year, sparking concern about the drug's effects on the brain. Prolonged exposure and abuse of substances such as heroin, meth, and alcohol can cause irreversible damage to brain function, especially when the abuse starts in youth. There is some evidence to support that the same may be true of marijuana abuse. 
Tetrahydrocannabinol (THC) is the primary psychoactive ingredient in marijuana. When someone smokes or ingests marijuana the THC attaches to the brain's cannabinoid receptors (cannabinoid receptor type 1 or CB1 receptor), affecting hippocampal neurons; the area of the brain that controls appetite, pain regulation, mood, and memory.
This leads to the person taking marijuana having a reduced ability to focus and recall important information. The length of time marijuana is smoked and in what quantity can lead to memory and concentration becoming impaired. Basic motor skills can also become impaired, making tasks such as driving more difficult and subsequently dangerous.
Despite the cognitive impairment from smoking marijuana, scientists are still conflicted about the long-term effects of marijuana on the brain. Some studies suggest regular marijuana use in adolescence is associated with a reduced volume of specific brain regions involved in a broad range of executive functions such as memory, learning, and impulse control compared to people who do not use.  However, other studies have not found significant structural differences between the brains of people who do and do not use the drug.
Does marijuana use affect IQ?
Studies into the link between marijuana abuse and a cognitive decline measured in IQ have largely reached inconclusive results. Some studies suggest marijuana abuse starting in adolescence that continues through into adulthood has a link to declines in IQ. 
The validity of this information is questionable though, especially when considering the variables that may affect the subjects of these studies such as family environment, genetics, age of first use, frequency and duration of use, length of the study, and whether a marijuana use disorder is present.
A large study in New Zealand found that continued marijuana abuse starting in adolescence resulted in IQ dropping 6 to 8 points in adulthood. The study also showed that those who abused marijuana heavily in adolescence but quit in adulthood did not recover IQ points and those who only started using marijuana in adulthood lost no IQ points at all.
Do THC edibles kill brain cells?
There is little research to suggest that consuming THC edibles is more or less likely to cause any long-term effects on brain function.
Weed edibles contain a synthesized (oil-based) form of THC which causes similar side effects to marijuana when consumed. This affects the way THC gets into the system as it takes longer for it to reach the bloodstream than if smoked.
Related blog: How Long Does Cannabis (THC) Stay in Your System?
As the amount of THC contained in edibles can vary greatly, how heavily it impacts cannabinoid receptors in the brain can also vary dramatically. While it is inconclusive how and if edibles kill brain cells, that they cause the same neurochemical reactions in the brain as smoking marijuana may be indicative of having similar negative side effects.
This is also true of cannabis concentrates such as shatter. More research is needed on these substances to accurately say whether they have a lasting effect on brain function.
Effects of synthetic marijuana on the brain
Synthetic marijuana (spice/K2) comes from a man-made hallucinogenic substance that is normally sprayed onto plant materials to replicate and enhance the effects of organic marijuana. Synthetic marijuana is not safe for human consumption but has become increasingly popular in recent years. The toxic components of synthetic marijuana, or “fake weed”, can cause increased heart rate, vomiting, bleeding, and produces powerful mind-altering effects.
Synthetic marijuana binds to the same cannabinoid receptors in the brain (CB1) as THC but far more intensely, making it at least 100 times more potent. CB1 receptors have multiple locations in the brain in both the central and peripheral nervous systems which makes the side effects of synthetic marijuana potentially intense and harmful.
Synthetic marijuana abuse may cause:
Cardiac and respiratory problems
Altered perception, or euphoria
Kidney and brain damage
Short-term effects of marijuana abuse on the brain
Difficulty judging distances
Long-term effects of marijuana abuse on the brain
- Some cognitive impairment
Some memory loss
Increased likelihood to use other drugs
Increasing marijuana tolerance
Poorer memory recall
Slower cognitive processing
Brain fog and trouble concentrating
Lower problem solving and critical thinking skills
Getting help for a marijuana problem
Marijuana is becoming increasingly accessible as more states move to legalize medical and recreational use, and public opinions are also changing, with many believing marijuana is harmless. This is not necessarily true, and there are some studies that indicate that marijuana use can negatively impact the body and also the brain, especially for young users, heavy users, and people who are long-term users.
There are treatment centers all over the country that are equipped to help those with a marijuana use disorder overcome the problem and begin recovery. If you or someone you know is suffering from a marijuana addiction, contact a treatment center today.