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Effects of Marijuana on the Brain

Effects of Marijuana on the Brain

Marijuana can produce a short-term sensation of elation and relaxation by acting on the central nervous system. This HealthHearty write-up gives you a brief idea about marijuana, and its positive and negative effects on the brain and other parts of the body.
Chandramita Bora
Last Updated: May 5, 2018
Did You Know?
The medicinal properties of marijuana were believed to be first discovered by the Chinese Emperor, Shen Nung in 2737 BC.

Marijuana, also known as cannabis or ganja, is obtained from the flowers, leaves, and the seeds of the cannabis plant. Hashish is the name of the sticky resin obtained from the flowers of the female cannabis plant. Marijuana contains almost 60 cannabinoids, the psychoactive compounds, of which the main active chemical is the THC or the delta-9-tetrahydrocannabinol.

Cannabis has been used by the mankind since ancient times. However, a growing trend of using it for recreational and medicinal purposes was witnessed in the 20th century. Many countries of the world prohibit the use, possession, and sale of this drug. However, the supporters of medical marijuana claim that weed can have several health benefits, if used in proper dosage. Let's find out how cannabis and its active compounds can affect the human brain.

Effects of Cannabis on the Brain

More than 400 different chemicals are found in the cannabis plant, of which 60 chemicals come under the category of cannabinoids. THC is the main cannabinoid that is responsible for producing the typical effects that weed users experience.

When marijuana is inhaled, the compound THC reaches the brain within a few seconds and activates its reward system. This is the reason why the users of marijuana experience euphoria and a sense of relief from stress or anxiety. The users often describe the effects of marijuana as somewhat relaxing and mellow.

In the brain, the compound THC binds to the cannabinoid receptors of the nerve cells. These receptors are normally activated by the neurotransmitter anandamide. Anandamide is actually a type of cannabinoid, just like THC. So, THC basically mimics the actions of anandamide by binding to the cannabinoid receptors present in the brain.

The cannabinoid receptors are mostly found in those regions of the brain, which control short-term memory, thought, coordination, sensation of pleasure, learning, and problem solving. A large of number of these receptors are present in the hippocampus, cerebellum, and basal ganglia. Located within the temporal lobe, the hippocampus is concerned with retaining short-term memory. So, a high level of THC can affect short-term memory or the ability to recollect recent events, by binding to the cannabinoid receptors present in the hippocampus.

THC can also bind to the receptors found in the cerebellum and basal ganglia, which are responsible for maintaining coordination and unconscious muscle movements respectively. So, THC can affect coordination (motor coordination) by acting on the cerebellum and basal ganglia.

Dopamine is the neurotransmitter that is known as the feel-good brain chemical, mainly because it activates the brain's reward system. THC can stimulate the brain cells to release dopamine, and thus produce a pleasurable sensation.

Apart from these, many people feel an increase in their appetite after smoking marijuana. This effect can also be attributed to the compound THC. THC is thought to increase appetite by interacting with the cannabinoid receptors present in the hypothalamus.

The Debate Over Cannabis

The Negative Effects

Some researchers have suggested a link between long-term use of marijuana and conditions, like anxiety, depression, bipolar disorders, and even schizophrenia. However, studies conducted in this regard are not very conclusive. In other words, not enough supportive evidence is available to establish the relation between marijuana and mental illnesses.

THC can induce both auditory and visual hallucinations, when it is taken in large doses. However, a massive dose of THC is required to produce complete hallucination.

In a 10-year study carried out in Germany, it was concluded that marijuana use can be a risk factor for developing psychotic symptoms. The study was carried out on 1,923 individuals in the age group of 14 to 24 years. According to this study, prolonged use of cannabis might raise the risk of psychotic disorder.

Recently, a study published in the Neuropsychopharmacology noted that the active compounds found in cannabis impaired the brain activities in young mice. The researchers exposed some young mice to very low levels of cannabis compounds for 20 days, after which they were returned to their families. They then studied the effects of cannabis compounds on the cortical oscillations of the adult mice, which were exposed to these compounds in their adolescence.

The scientists observed a change in the cortical oscillations and cognitive abilities of those mice. So, the damage caused by the cannabis compounds in those young mice actually continued into their adulthood. The scientists carried out the same experiment on adult mice by exposing them to cannabis compounds. Surprisingly, their cortical oscillations and cognitive functions remained same or normal. This indicated that the exposure to cannabis only during adolescence impaired brain activities in mice.

Another concern raised against the use of marijuana is that the chronic exposure to THC may speed up the age-related loss of neurons in the hippocampus. A loss of hippocampal neurons can reduce the ability to learn new skills, which is why elderly people find it more difficult to learn new things. The effects of THC on hippocampal neurons have been observed in an animal study, wherein some rats were exposed to THC for 8 months. It was observed that the loss of nerve cells in those rats were equivalent to those observed in rats twice their age.

The Positive Effects

The cannabis plant has been in use for medicinal purposes for a long period of time. So far, medical cannabis has been legalized in several states of the United States, Canada, and five European countries, when it is recommended for pain relief, nausea, and for relieving certain symptoms associated with chronic illnesses. Both Colorado and Washington have even legalized the recreational use of marijuana. Several studies have also been carried out to find out the positive effects of THC and other cannabis compounds, and many of which have noted that these compounds can actually have some positive health effects.

A research done by the Scripps Research Institute in California have found that THC present in marijuana can help prevent the formation of "Alzheimer plaques" in the brain. The formation of these deposits are found to be accelerated by an enzyme, known as acetylcholinesterase. THC has been observed to prevent acetylcholinesterase from doing this, and thus slow down the progression of Alzheimer's disease. THC may also reduce oxidative stress, and inflammation of the neurons.

Marijuana can help prevent, as well as treat glaucoma, by reducing the pressure in the eyeball (intraocular pressure). Glaucoma can damage the optic nerves and impair vision. Several studies have noted the effectiveness of cannabis in preventing or alleviating nausea and vomiting induced by chemotherapy as well.

A study conducted by Complutense University of Madrid has observed that the chemical compounds present in cannabis can promote the death of cancerous cells by inducing autophagy. In fact, THC has been found to have anticancer effects in mice with human brain cancer cells. The cancerous tumors were found to shrink in size after receiving THC, while the healthy cells remained intact. The anticancer effect of THC was also observed in people with brain tumors.

So far, two studies, one conducted in 2007 and another in 2010, have found that cannabidiol found in marijuana can prevent the spread of breast cancer to other parts of the body, without producing any debilitating side effects unlike chemotherapy. Cannabidiol has been observed to block the activity of a gene (ID1) that is believed to be associated with metastasis. These studies were carried out at the California Pacific Medical Center Research Institute.

Though several studies have been conducted to find out the effects of continuous or long-term use of cannabis on the brain, their results are largely inconsistent. So, we have limited understanding about the long-term effects of marijuana on the brain. Only future research in this area can give us a definite answer whether marijuana is addictive or whether it has any adverse effect on the brain. However, its regular use at an early age is largely believed to be associated with an increased risk of mental illnesses.

Disclaimer: This article is for informative purposes only, and should not be treated as a substitute for professional medical advice.