What does THC do to the brain?

Marijuana is a controversial topic in modern-day society. Many support it as a universal painkiller with healing properties that help with most conditions. Others are staunch supporters of the theory that weed causes irreparable damage, especially to the brain and the central nervous system. Both the positive and the negative effects can be contributed to a multitude of compounds, but first and foremost to THC or tetrahydrocannabinol. What does THC do to the human brain to make such a significant impact?

What is tetrahydrocannabinol?

Also known as THC, this is the strongest active compound of cannabis. THC is the compound responsible for the high effect that marijuana and cannabis products are known for. It has multiple medical benefits in relieving the symptoms of glaucoma, insomnia, anxiety, muscle spasticity, and a few others. However, THC carries some severe side effects like memory loss, coordination problems, slower reaction times, seizures, and seizure-like activity. Multiple studies suggest that it can even lead to depression, anxiety, schizophrenia, and substance use disorders.

Chemical structure

THC has a molecular structure of 21 carbon atoms, 30 hydrogen atoms, and two oxygen atoms. It shares a high similarity to the endocannabinoids – metabolites that take care of the central nervous system. This is the source of THC’s high activity. 

Impact of THC on the human brain

Tetrahydrocannabinol affects the human brain through the endocannabinoid system. There, THC affects the cannabinoid 1 receptors (CB1). 

The endocannabinoid system

The ECS is a huge network of chemical signals and cellular receptors. It is involved in regulating phycological and cognitive processes like appetite, pain,  memory, and mood. Its primary receptors are CB1 and CB2 are the main targets of cannabis compounds such as THC and CBD. 

The ECS is then overwhelmed by the attached THC, which sends the whole system into disarray by interfering with the brain’s natural cannabinoids. This results in the popular sensation of being high and a wide range of unwelcomed side effects.

The negative effects of THC on the brain

The effect known as high is the result of THC stimulating the same response from the brain like food and sex, unleashing a wave of dopamine. However, the list of unwanted side effects is lengthy. Some of them are short-term, while others can be lengthy and can affect more than one aspect of the smoker’s health.

Mental Health and Thinking

Many smokers experience negative side effects like anxiety, depression, and panic attacks. In the long term, marijuana can lead to clinical depression and paranoia. 

It can also blur one’s senses and judgments, distorting the sense of time and motor skills. 

Brain impairment

One of the things that THC does to the brain is a short-term lack of focus. However, smoking marijuana in one’s teens can lead to severe learning and memory disabilities. 


It is a popular belief that marijuana is not addictive. However, about 10% of those that smoke can get hooked. It is a physical dependency with heavy withdrawal effects. 

Lung and heart damage

The smoke can lead to lung damage and irritations, as well as long-term breathing problems. Also, THC is known to weaken the immune system of users. 

THC can further increase heart rate. Many cases document an increase of up to 120 beats per minute.

Positive effects of THC

Despite all its negative effects, THC is known to have a lot of positive effects on the human body and brain. 

  • THC can reduce inflammation;
  • It is often used to treat drug and alcohol;
  • Excellent treatment for anxiety disorders;
  • It can be used to treat gastrointestinal (GI) disorders;
  • Good for treating epilepsy and other seizure syndromes.


Researchers are divided when it comes to cancer – many researchers suggest that THC can prevent cell growth and induce cell death, while others suggest that it can be linked to cervical, prostate, and bladder cancer. 

THC and brain cells

There are multiple conflicting studies in terms of THC, marijuana, and brain cell damage – whether it is the THC that affects the cells in a negative way or the way it is received, be it as a vape, by smoking, or edibles. 

A popular study from New Zealand stated that people who started using marijuana as teens lost an average of six to eight IQ points when they reached adulthood. Those who stopped at some point did not regain these IQ points back. However, users that started smoking as adults didn’t suffer from IQ decrease. 

This was one of the first large-scale studies. However, it did not rule out additional factors that may lead to a decline, like genetic factors. 

Another factor that many consider is age. The quoted study suggests that an adolescent brain (of a person under 25 years) can be severely damaged by marijuana and THC in particular. 


There’s a plethora of negative side effects suggested by a large number of studies. These side effects can range from memory and attention deficits, and structural brain changes. Long-term use was suggested to lead to a decrease in IQ functions.

Further researches suggest that early marijuana use can lead to heavy mental conditions like major depression and schizophrenia.


The effects of THC on the adult brain are less clear. Fewer studies were conducted and some of them suggest that the brain of a person older than 25 years is exposed to the same risks as the younger one. 

However, a good amount of studies suggest that the risks are much smaller (if any) than those that the adolescent brain can suffer. 

In conclusion

What does THC to the brain is yet to be decided? Many studies suggest beneficial effects like reducing anxiety and depression, along with beneficial effects in treating quite a few forms of cancer. On the other hand, many researchers provide information on heavy forms of brain damage, a huge decrease in brain and IQ functions, and even severe mental disorders and depression. 

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