Marijuana Effects on the Brain: The Ultimate Guide

As the legalization of marijuana for recreational and medical use slowly ekes out one state after another, it has become very important to understand its impacts on the brain.

At the moment, weed is legal for recreational use in 10 states and Washington, DC. The land of Lincoln is expected to be the 11th state to wave the green flag on the legal use of pot by January 2020. And judging from the trend, it’s very likely that we’ll have 10 more states joining the bandwagon by next year.

Basically, we’re now moving the conversation from ‘’is weed good or evil’’ to ‘’long term and short term marijuana effects on the brain.’’

Let’s take a deeper look at this coveted drug.

How does Marijuana Work in the Brain

First, let’s have a short lesson on neuroscience.

The human brain comprises of a complex system of neurons and neural circuits known as the Endocannabinoid System (ECS). The word ‘’Endocannabinoid’’ is derived from 2 words;

So, the Endocannabinoid System basically refers to cannabis-like substances that naturally occur inside our bodies.

The ECS is made up of 4 core components that work together;

Endocannabinoids – these are molecules that are pretty much similar to the cannabinoids that are found in weed only that they are naturally made by the body. They are sent from one neuron to a target neuron in the form of a chemical message.

There are currently 2 key endocannabinoids that neuroscientists know of so far; Anandamide (AEA) and 2-arachidonoylglyerol (2-AG).

Neurotransmitters– your brain cells like keeping a distance from each other. For messages (endocannabinoids) to pass the gap between the cells, they need to be carried by chemicals called neurotransmitters.

Endocannabinoid Receptors – as the name suggests, the receptors are responsible for ‘receiving’ the endocannabinoids.

There are 2 types of receptors; CB1 receptors (found in the Central Nervous System) and CB2 receptors (found in the Peripheral Nervous System- outside the brain and spinal cord).

The Endocannabinoids can bind to either of these receptors depending on the message. And this also means that the resultant action will depend on where the receptors are located.

Enzymes– the enzymes in the ECS are responsible for breaking down the endocannabinoids after completing their function.

The Endocannabinoid System has an array of physical and mental functions including learning and memory, sleep, motor control, mood, appetite and digestion, muscle formation, and stress management.

Marijuana Effects on the Brain

When you consume marijuana, THC (tetrahydrocannabinol- the key psychoactive ingredient of weed) enters the blood system and zips all over the body including in the brain.

Since this marijuana cannabinoid looks exactly as the cannabinoids that the body produces and actually acts in the same manner, it is able to bind to the cannabinoid receptors.

THC is powerful. Thus, it overwhelms the natural endocannabinoids and thereby prevents them from carrying out their usual role of relaying communication between the neurons.

Resultantly, the natural balance of the endocannabinoid system is thrown out of whack. It alters the signals by boosting some and completely blocking others. This partly explains why the effects of marijuana range from a cool feeling of relaxation (High) to clumsiness and anxiety.

Parts of the brain that are highly affected by THC

Once in the brain, THC affects pretty much all the regions that have CB receptors. Worth noting, the impacts on each of these areas range from high to moderate depending on the number of receptors. That’s to say that parts of the brain that have the highest number of cannabinoid receptors tend to experience the highest level of disruption.


The cerebellum is located at the back of the top part of the brain- precisely, where the brain and spinal cord meet. It receives signals from different parts of the brain, the spinal cord, and other sensory systems.

The cerebellum is responsible for the body’s balanced muscular movements and, therefore, coordinates voluntary movements such as posture, coordination, balance, and speech.

Worth noting, although the cerebellum is a relatively small part of the brain at around 10% of its total weight, it boasts roughly 50% of the brain’s neurons. This means that it is hit the hardest by THC resulting in impaired coordination.

Basal ganglia

The basal ganglia is a forebrain system that constitutes a number of organs including the cerebrum, substantia nigra, midbrain, putamen, and caudate.

While each of these parts has specific roles of their own, when viewed as one complex network, their major role is to control movement. Put in simpler terms, the basal ganglia facilitates movements and also inhibits competing movements.

Considering all the parts that make up the basal ganglia, it’s not surprising that it also has a high concentration of CB1 receptors.

When THC binds to the receptors in this system, an individual will generally exhibit problems starting a movement, that is, slowed reaction time. In addition, one may experience muscle spasms, tremors, and problems controlling speech.


This is an important formation of the brain that is responsible for memory. And this encompasses everything from learning to converting short-term memories to long-term memories for storage in another part of the brain.

The hippocampus has also been found to play a significant role in spatial navigation (learning new information) and spatial memory. This function is what helps a driver to learn, memorize, and remember streets in a busy city.

Since the hippocampus has a key role in learning and storage of new information, the binding of THC to its receptors leads to impaired memory.

Areas of the brain that are moderately affected by THC


This refers to an almond-shaped section of the brain located at the back of the hippocampus. Its key role is to perceive emotions including fear, anxiety, anger, and sadness.

The amygdala is what makes us fear things that are out of our control and it’s responsible for how we react towards certain stimuli.

This part of the brain also helps in storing memories of past events so that one can recognize similar occurrences in the future and take the necessary measure.

Interestingly, the amygdala is popularly known for its role in processing fear. Actually, it is usually connected directly to the thalamus by a special pathway- and this makes it possible to relay fearful stimuli directly to the amygdala even before it’s processed in the cortex. Consequently, we react to fearful stimuli even before we’ve thought about it.

After consuming marijuana, the cannabinoids have been found to help in dampening excitatory signals that cause anxiety. This explains why most weed users claim that it helps them in dealing with anxiety.

However, it’s quite paradoxical that chronic use of weed usually down-regulates the receptors thereby increasing anxiety, panic, and paranoia.


The neocortex occupies the largest part of the brain- around 76% by volume. It is responsible for higher functions including generating motor commands, sensory perception, conscious thought, spatial reasoning, and language.

Research results have shown that THC usually disrupts the neural circuits in the cortex. This could lead to altered judgment, thinking, and sensation.


The hypothalamus is a small but very important part of the midbrain that is responsible for homeostasis- that is, maintaining the body in a stable and balanced state at all times.

The hypothalamus acts as a link between the nervous and endocrine systems and receives signals from all over the body. It responds to unbalanced factors such as hunger, thirst, emotions, sleep cycles, body temperature, appetite, weight control, heart rate, blood pressure, and sex drive among others. It also responds to stressful stimuli by signaling the production of cortisol- the stress hormone.

The hypothalamus has CB1 receptors that receive chemical messages from endocannabinoids. When you consume weed, THC sets in as a boost of the number of cannabinoids that are sent to the hypothalamus. An increase in the cannabinoids that send the ‘’I’m hungry’’ messages usually increases appetite or what is known as the munchies.

How long does marijuana take to kick in and reach peak levels in the brain

The time you take to peak after consuming weed largely depends on the mode of administration although there are some other secondary factors.

There are different ways of administering cannabis but inhalation (smoking joints and bongs and vaping) and edibles (cooked into food) are the most common. Other methods include topicals (using it in the form of sprays and lotions), and tinctures (alcoholic solution).

Regardless of the mode of administration, the cannabinoids including THC (the psychoactive component of weed) need to get to the brain to cause the ‘High’.


When you smoke or vape weed, the smoke/vapor goes to the lungs where THC is absorbed directly into the bloodstream.

Immediately after entering the bloodstream, THC travels to the heart where it is pumped throughout the body including the brain where it binds to the cannabinoid receptors.

Smoking and vaping are the most efficient ways of administering weed and the High should kick in 5-15 minutes later.


The weed takes a different pathway when consumed through edibles such as cookies or brownies. When ingested, weed is digested and THC is absorbed into the bloodstream via the stomach lining. Ingestion is very effective and studies show that up to 95% of total THC is absorbed.

After entering the bloodstream gastrointestinally, THC is carried to the liver first where a good chunk of it is either metabolized or eliminated. Some of it, however, is released into the bloodstream again where it circulates around the body including in the brain.

The absorption of THC through the stomach walls isn’t as fast as in the lungs. This, coupled with the fact that the absorbed THC has to go through the liver first prolongs the time that it reaches the brain.

Generally, the onset of the ‘High’ feeling after ingesting weed could take 30 minutes and should peak after 2.5-3.5 hours.

Marijuana effects on the cells

There is a very heated debate at the moment on whether or not marijuana kills brain cells. The source of this debate is a popular 2012 study that found a correlation between the use of marijuana and cognitive decline.

This study involved following over 1000 marijuana users aged 13 to 38 years for a period of 38 years and found out that;

This study generally suggests that marijuana may have irreversible effects on brain development among adolescents.

Although there are several researchers who side with these findings and conclusion, most of them feel that there are a lot of other factors that could have led to cognitive decline and which the study didn’t rule out. These include personality factors such as low consciousness when taking the test on cognition and socioeconomic status.

Actually, another 2016 study didn’t find any differences in IQ decline between twins who used weed and their siblings who didn’t.

While there’s still a lot that needs to be done to clear the confusion around this issue, there’s almost no evidence that the active ingredients in weed have neurotoxic effects. This is unlike alcohol which upon digestion leads to the creation of metabolites that have been known to be toxic to brain and body cells.

Long-term and Short-term effects of weed

Most recreational stoners are generally after the classic uptick in emotions and physical energy that weed causes (a.k.a the High feel).

But this fascinating drug has a couple of other effects that can be short term or long term, and either positive or negative.

Short term effects

These are effects that occur as a result of the high that weed causes and they usually cease shortly after use.

Positive short term effects

  1. More intense emotions – for instance, increased fun. Note that you can also feel an intense feeling of fear. It all depends on what you carry.
  2. Relaxation – marijuana is thought to help in easing feelings of anxiety and fear because THC binds to receptors in the amygdala. This reduces the brain’s response to a threat.
  3. Pain relief – Marijuana’s ability to relieve chronic pain albeit temporary is among the key reasons why it’s legal for medical use in 33 states. The relationship between marijuana use and chronic pain is strongest especially with cancer-related pain and nerve pain (neuropathy). It also helps patients with multiple sclerosis by improving muscle spasms.
  4. Elevated senses of touch, smell, hearing, seeing, and tasting
  5. Unusual much laughter
  6. Increased brain activity leading to creative ideas

Note here: it’s important to mention that these positive short term effects may vary between users. There are lots of factors in play here including the quality of weed in terms of THC concentration and how often the user takes weed (those who take seldom make experience most of these effects).

Negative short term effects

  1. Cottonmouth (dry and sticky mouth) – When you smoke weed, THC binds to the receptors in the brain and others that are found in the submandibular glands in the mouth. This leads to effective relaying of chemical messages thereby leading to a decline in saliva production.
  2. Red-rimmed eyes – The reason why an individual’s eyes turn red after consuming marijuana is that THC causes a fall in blood pressure. This causes the blood vessels in the eyes to dilate and stand out. In effect, they receive a massive flow of oxygenated and nutrient-rich blood.
  3. Memory loss – While weed won’t lead to memory loss, it alters your mind’s ability to form new ones. This is because it binds heavily on the hippocampus- a section of the brain that is responsible for memory formation.
  4. Impaired motor control – Disrupted motor control is one of the signature short term effects of weed. And this explains why it’s illegal to get behind the wheel under the influence of marijuana. The largest concentration of cannabinoid receptors in the brain are found in the substantia nigra and striatum. These are the sections that are involved in movement coordination- a vital skill in driving.
  5. Increased heart rate – After consuming weed, you will experience a spike in blood pressure which consequently leads to an elevated heart rate of up to 50%. This has been found to occur about 15 minutes after smoking which leads to the conclusion that it is caused by the activation of cannabinoid receptors in the brain. This spike could last for up to an hour and research results show that it increases your risk of a heart attack by 4.8 times.

Long-term effects of Marijuana

Positive effects

With all the negative side impacts of weed that are used to demonize it, you’ll not be alone if you didn’t know that there are a couple of long-term positive effects of taking weed.

Helps in re-growing brain cells

As mentioned earlier, cannabis has for long been thought to kill brain cells. But in this study, the researchers found out that the CBD in cannabis actually caused the growth of the brain cells in the hippocampus in rats and mice.

In human beings, researchers argue that this ability could help in dealing with anxiety, stress, and depression since the hippocampus is responsible for regulating emotions.

Homeostasis- (body balance)

Since the cannabinoids in weed look and work exactly as the body’s endocannabinoids, researchers opine that cannabis can be used to deal with disorders that are related to endocannabinoid deficiency.

The endocannabinoid system is generally responsible for homeostasis- maintaining body balance by countering factors such as hunger, thirst, sleep, body temperature, appetite, and emotions among others.

A deficiency in the body’s endocannabinoids could not only make the body unstable, but it could also lead to other complications including illnesses. This is because homeostasis also maintains a healthy immune system too.

Negative effects

Lung damage

With all the smoke that one has to inhale, it’s not surprising that lung damage is one of the long-term effects that come with smoking weed.

The smoke from marijuana destroys the cell lining of the airways thereby putting the lungs at the risk of germs invasion, infections, and dust.

Can cause infertility in men

Although the effects of marijuana on female fertility are currently inconclusive, there is enough evidence that THC reduces sperm motility in males. Researchers have also noted that it affects the production of testosterone. These 2 could lead to infertility.

Anxiety and Depression

Although weed is commonly taken to reduce anxiety on a short term basis, it’s counterintuitive that early marijuana use (among adolescents) increases the risk of developing psychiatric disorders such as anxiety and depression later in life.

What happens to the brain after quitting weed

Researchers aren’t exactly sure what happens to the brain once a marijuana user starts the process of being ‘clean.’ But it’s well documented that as the brain tries to rewire, an individual experiences withdrawal symptoms such as vivid dreams, anxiety, poor sleep, irritability, physical tension, and emotional jags.

It’s also very common to experience ‘using dreams’ (dreams about taking weed) – and these are known to last for years.

Some people also display loss of concentration usually 1 week or month after abstinence which consequently affects learning ability for a short while.

How to restore brain from marijuana use

Restoring a brain that has been used to marijuana use to normalcy isn’t always an easy task, but that does not make it impossible.

The brain is constantly restructuring depending on the changes that you take it through including having weed and not having it.

Unfortunately, there isn’t much that you can do to fix the brain instantly from the unfortunate changes that pot made. It’s not as easy as fixing a bike chain.

The good news, however, is that you are in direct control of the recovery program. This basically means that your decisions, actions, and reactions on the effects of quitting and moving on will impact how the brain rewires itself.

All your brain needs from you is the desire and will to pick up the broken pieces and set things right again. The first- and very important- step to recovery is finding a social group that doesn’t do drugs. Of course, your best bet here is joining a group of people who’ve had a similar experience and are determined and hopeful to solve a common problem.

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