As marijuana legalization efforts continue across the globe, sometimes outrageous claims, are being made both by proponents and opponents about the use of this controversial plant.
While proponents of marijuana legalization are pointing out its countless positive effects, opponents of marijuana legalization are pointing out its dangerous effects.
Who's telling the truth? Who's right?
Because the brain is the control chamber of the human mechanism, and almost every effect caused by marijuana is based on the chemical changes that happen in the brain…
To really understand the effects of marijuana, we have to look at how it affects the brain.
Today you're going to learn:
Marijuana's immediate and long-term effects on the brain.
But in order to really understand what's marijuana's effect on the brain, first, we have to understand how marijuana affects your brain.
Important note: If you decide to use cannabis medically or recreationally, make sure to use a dry herb vaporizer and NEVER smoke cannabis ever again. Although a dry herb vaporizer won't protect you from marijuana's negative effects on the brain, it will reduce your exposure to toxins that are created when you burn cannabis flower.
How Does Marijuana Affect Your Brain?
Even though THC is the most well-known compound of the marijuana plant (or Cannabis plant), this complex plant contains over 500 known compounds, and probably many unknown compounds.
Now, what really sets marijuana apart from the other plants in the vegetable kingdom, is a specific type of compound only found in the marijuana plant:
Cannabinoids are compounds mainly responsible for the effects of marijuana.
Why do I say mainly?
Because there are other types of compounds in marijuana as well, like terpenoids and flavonoids, and research suggests that these ‘other’ compounds have a separate effect on your mind and body (different than the cannabinoids), plus influence the effects of cannabinoids as well (1).
But cannabinoids are the main compounds that need to be looked at, to understand marijuana's effect on the brain.
And of all these cannabinoids, THC is the one that has the most profound effect on your brain. THC is currently the only known psychoactive cannabinoid in marijuana and the cannabinoid that is responsible for your ‘high’.
How Do Cannabinoids Affect the Brain?
Your brain has specific cannabinoid receptors, and cannabinoids act on these receptors in different ways (for a detailed discussion on how this process exactly works, click here).
A simplified version of how cannabinoids affect the brain:
By acting on these brain receptors, cannabinoids change your brain chemistry temporarily. For example, cannabinoids can:
- Activate brain receptors, stimulating the activity of neurotransmitters that communicate with these receptors or;
- Bind to these brain receptors, inhibiting the uptake and increasing the presence of certain neurotransmitters in the brain.
This holds true especially in particular parts of the brain where the amount of these cannabinoid receptors is larger than in other parts.
Cannabinoid receptors in the brain are mainly located in (2):
- Forebrain areas related to higher cognitive functions;
- Forebrain, midbrain, and hindbrain areas related to the control of movement, and;
- Hindbrain areas related to the control of motor and sensory functions of the autonomic nervous system.
By acting on the cannabinoid receptors in these brain areas, the cannabinoids found in marijuana cause chemical changes in your brain that can result in:
- (Neuro)protective effects;
- Changes in your psychomotor abilities;
- Changes in your cognitive processes;
- Changes in your perception, mood, and consciousness (psychoactive effects), and;
- Potential physical changes in your brain in the long term, even when you aren’t under the influence of any marijuana.
Then there’s the distinction that has to be made, between acute (short-term) and long-term effects of marijuana on the brain.
Long-term effects are harder to reverse than short-term effects. If marijuana has the potential to alter your brain chemistry in the long term (spoiler: which it has), it’s important that you’re careful with its use.
First, we start with the:
Acute Effects of Marijuana on the Brain
The acute effects of marijuana are the effects that are immediately noticeable.
And the reported acute effects of marijuana on the brain are plenty, but all of them can be categorized in:
- (Neuro)protective effects;
- Psychomotor effects;
- Cognitive effects;
- Psychoactive effects.
Also, the acute effects, especially the psychoactive effects, are more subjective and individual than the long-term effects on the brain.
About the short-term effects of marijuana, studies can only speak in generalities. For example, most studies find that the concentration of people under the influence of marijuana worsens. But you’ll also find anecdotal reports of marijuana users saying they improve their concentration by using it.
The acute effects of marijuana are also highly dependent on variables like:
- Mode of use (smoking, vaping, eating),
- The strain,
That said, let’s take a look at what the studies are showing.
Acute (neuro)protective effects of marijuana
Marijuana has the potential to protect your brain and its neurons, immediately when you use it, both against the effects of acute trauma like brain injury and against the effects of long-term neurodegenerative diseases like Alzheimer’s disease.
According to a study done in 2014, that compared mortality rates of patients that suffered from traumatic brain injury, patients that had screened positively for THC (greater than 50 ng/mL) had a significantly lower mortality rate (3).
This finding implies that THC has a neuroprotective effect, and supports earlier findings mentioned in the same study that found neuroprotective effects associated with cannabinoids.
A 2010 study explored the potential of cannabinoids in treating neurodegenerative diseases like Parkinson’s disease and Multiple Sclerosis (4). The main conclusion of this study was that cannabinoids and cannabinoid-based medicines that target CB receptor ligands, but especially CB2 receptor ligands, have the most potential in treating neurodegenerative diseases. CB2 receptor ligands have an important role in regulating neural inflammation and neurogenesis, and they're targeted by the cannabinoids like THC and CBD found in marijuana.
Neurogenesis is the process by which new neurons are generated in the brain, and it seems at least some compounds in marijuana have the potential to help this process.
In a study done in 2013 that looked at the anti-anxiety effects of CBD, Brazilian researchers found that the cannabinoid CBD increased neurogenesis, specifically in the hippocampus in mice (5). Even though these findings aren’t directly translatable to humans, they do show potential. Just keep in mind that most marijuana strains currently on the market are very low on CBD.
ALSO READ: The Best CBD Oil for Anxiety
CBC is another cannabinoid found in marijuana that could potentially help neurogenesis. A study done in 2013 found that CBC has a positive effect on the viability of ‘adult neural stem progenitor cells’ in mice (6). So again, this study is done on animals and is not directly translatable to humans, but it shows the potential of the cannabinoids found in marijuana in neurogenesis.
Acute effects of marijuana on psychomotor skills
Since cannabinoid receptors are abundant in the basal ganglia and cerebellum (particular parts of the brain), and these parts are associated with psychomotor skills, it’s no coincidence that the use of marijuana has an immediate effect on your psychomotor skills.
Most studies that looked at the effects of marijuana on psychomotor skills found that especially THC has the potential to impair psychomotor function (7).
Most of the studies that looked at the acute effects of marijuana on psychomotor skills found that:
- The more THC is in your system, the worse the impairment, and;
- The less frequent you use marijuana, the worse the impairment (essentially the lower your tolerance, the worse the impairment).
In a meta-analysis of 150 experimental studies that looked at the effects of marijuana on physical activity, researchers found that smoking marijuana acutely impaired (to different extents) the following physical performance areas (8):
- Psychomotor skills;
- Divided attention;
- Visual functions;
- En- / Decoding
- Reaction time.
How does this information apply to your marijuana use?
It’s clear that marijuana can severely influence your psychomotor skills and reaction time.
NEVER drive while under the influence of marijuana. Especially the first few hours after smoking/vaping it your psychomotor skills, attention, and reaction time can be severely impaired.
Besides driving, just avoid any type of physical activity in which it’s possible to hurt yourself or others and which needs a high level of attention, reaction time and/or a high degree of psychomotor skills.
Acute effects of marijuana on cognition
Cognitive functions are the functions in your brain that enable you to acquire, process, and act on incoming information (attention, memory, decision making, etc.).
These are very essential skills for even basic survival. It’s no coincidence that a lot of research on the effects of marijuana on the brain is looking at the effects on specific cognitive skills (also this is somewhat objectively testable compared to subjective psychoactive effects).
What is the current state of affairs with regards to the acute effects of marijuana on cognitive skills?
With regards to the effects of marijuana on cognitive processes, all ‘facts’ in this article are based on the 2 largest systematic review studies which analyzed over 50+ studies that looked into this topic (both acute and long term effects of marijuana on cognitive function):
- A 2003 study “Non-acute (residual) neurocognitive effects of cannabis use: A meta-analytic study” (9), and;
- A more recent 2011 study “An Evidence-Based Review of Acute and Long-Term Effects of Cannabis Use on Executive Cognitive Functions” (10).
In an analysis of 5+ experimental studies which focused on the acute effects of marijuana on attention/concentration researchers from the 2011 study found mixed results (10):
- Infrequent users of marijuana can experience some impairment in their attention and concentration skills, however,
- Heavy chronic users actually got better at attentional processing when they were under the influence of marijuana.
A possible explanation the researchers give for these results is that chronic use of marijuana may result in your brain adapting to the marijuana exposure in such a way, that your brain actually normalizes while under the influence of marijuana.
What does this mean for you?
First, it means that in some cases, heavy marijuana use alters your brain chemistry in such a way that your brain ‘needs’ marijuana to function properly. This is quite alarming and something I would like to avoid at all costs.
Second, it means that if you’re a recreational user, you have to be careful of partaking in activities that require a high level of attention in which you may hurt yourself or others (i.e. don’t go operate the air traffic control tower under the influence of marijuana…if you happen to work there).
Decision-making and risk-taking
Here the current state of affairs is again mixed.
With regards to risk-taking, there are studies that find acute intoxication with marijuana can lead to increased risk-taking. However, there are also studies that don’t find such a correlation (all of these studies can be found in the 2 systematic review studies linked above).
With regards to decision-making, it seems there are as many studies that find no impairment on the ability to make the right decisions, as studies that do find such an impairment. One thing most studies do find though is that the process of making a decision slows down significantly.
Other than the fact your decision-making process will slow down, marijuana use could lead to an increase in risky behavior as well.
This is one topic where almost all studies and researchers are on the same page:
- Marijuana use does immediately and significantly impair working memory.
This again means that it’s not advisable to partake in activities that require a high level of attention in which you may hurt yourself or others when you’re under the influence of marijuana.
Verbal fluency is the ability to generate words in a set amount of time. And according to the 2011 systematic review study, the acute effects of marijuana on the brain do not seem to influence your ability to speak fluently (10).
However, according to the 2003 systematic review study, marijuana use does seem to have a small impact on your verbal / language skills (11).
In other words:
The results of the studies that looked at the effects of marijuana on verbal fluency are mixed.
Psychoactive (the high)
The acute effects of marijuana on the brain result in the ‘high’.
This feeling that we call the ‘high’ is subjective. But when a lot of people report the same types of feelings during a high, it starts to get ‘factish’.
In the largest study that looked into the reported psychoactive effects of marijuana (12), the most common reported feelings were:
- Sensory alteration;
- Changes in appetite;
- Changes in perception of time;
- Clearer thinking;
- Exaggeration of mood.
There are also common negative feelings being reported:
Some users would like to know:
How do you avoid these acute negative effects?
Ultimately, you’re going to have to experiment with the following variables:
- Your mode of use (I prefer vaping);
- Your marijuana strain (I prefer Sativa strains);
- Your set and setting (I only vape marijuana when I’m already in a good mood, and in a calm environment)
And find your own sweet spot regarding the effects.
Important to note here is that research has shown that the right amount of CBD can counteract the acute negative effects that are mostly associated with THC (like anxiety).
Long Term Effects of Marijuana on the Brain
‘Long-term’ effects of marijuana (in most studies) are the effects that occur/are observable/remain:
- 21+ days since last using marijuana.
Physical changes in the brain caused by long-term marijuana use
The physical changes in the brain refer to brain volume and the increase/decrease of specific types of brain substances like gray matter and neurons.
Heavy and chronic use of any psychoactive substance has the potential to change your brain volume and brain chemistry in a significant way.
But is there any evidence for marijuana?
Currently, there’s one brain part where researchers found that heavy and frequent marijuana use can lead to a significant reduction in the volume of gray matter:
- The hippocampus.
This finding is based on the largest systematic review study, which scrutinized the results of 14 studies that looked into structural brain alterations caused by marijuana (13).
The hippocampus is mainly associated with short-term memory, long-term memory, and spatial navigation. This means that heavy and frequent marijuana use can negatively influence all of these brain functions.
(Neuro)protective effects related to long term marijuana use
Science has shown that certain compounds in marijuana have strong (neuro)protective effects on the brain. And according to some studies marijuana has the potential to be used as a treatment for various diseases that have their origins in the brain.
In a study done in 2008, researchers found that the most well-known compound in marijuana: THC, is a considerably superior inhibitor of Aβ aggregation than currently approved drugs prescribed for the treatment of Alzheimer’s disease (14). Aβ aggregation is the key process that leads to the loss of neurons in Alzheimer’s disease.
A more recent study in 2014, also confirmed that THC is effective at lowering Aβ aggregation at extremely low concentrations in a dose-dependent manner (15).
The 2 most well-known cannabinoids in marijuana:
- THC, and,
Have been shown to stop the growth of one of the most aggressive cancers in adult humans: glioma (a specific type of brain cancer) (16). THC and CBD have been shown to be especially effective in stopping the growth of glioma when combined with traditional radiotherapy.
Effects of long-term marijuana use on cognition
The current state of affairs with regards to the long-term effects of marijuana on cognitive skills are anything but clear and conclusive (like many, many things in science).
According to the 2011 systematic review study that looked into the effects of marijuana on cognitive skills, there seems to be no effect of marijuana in the long term, on basic attentional and working memory abilities (10).
But there seems to be an impairing effect on:
- Concept formation, and,
Especially users who either:
- Started early (before they were 17), and/or;
- Used marijuana heavily (daily and/or large quantities of marijuana),
Experienced strong impairing effects on decision-making, concept formation, and planning.
Effects of long-term marijuana use on mental health
You don’t need to be a researcher to understand that chemical changes in your brain over a long period of time, could lead to mental imbalances.
But is there any actual evidence of marijuana use leading to long-term mental imbalances?
There have been numerous studies and systematic review studies that have looked into this topic.
And the results are again mixed.
Psychosis and affective diseases (mood disorders)
Researchers of the largest systematic review that looked if there was any relationship between the use of marijuana and psychosis and mood disorders, found that marijuana use can increase the risk of developing a psychotic illness and affective diseases later in life (17). According to the researchers, the risk increases 1.4 times compared to non-users.
There are 3 factors that seem to highly contribute to such a risk:
- Existing susceptibility to psychotic illnesses;
- The onset of marijuana use in adolescence years (before 18), and;
- Heavy and frequent use of marijuana.
Be extremely careful with using marijuana if you think you might be susceptible to any form of psychotic disorder.
General psychological issues
Besides looking specifically at psychosis and mood disorders, there have been many studies that looked at an association between marijuana use and general psychological health issues.
In the largest systematic review of at least 16 studies that looked at the relationship between marijuana use and general psychological health issues, researchers found mixed results (17).
In the end, the researchers essentially conclude cannabis use is associated with an increased risk for psychotic disorders and affective outcomes like depression and anxiety, although the link between cannabis use and affective outcomes like depression and anxiety remains weak. The researchers also found that high doses and frequent use of cannabis were more strongly associated with psychotic disorders and affective outcomes later in life.
Any causal links between marijuana use and mental health issues have not been proved yet. But this doesn’t mean that there aren’t any. Be careful, especially with heavy and frequent marijuana use.
My Personal Thoughts on These Results:
Important to mention is that in most studies where any long-term effects were found, users had the following characteristics:
- They started at an early age (before 17), and/or;
- Used marijuana heavily (daily and a large amount of marijuana).
This is all makes very much sense when you look at the fact that the human brain is still developing heavily in many areas during adolescence. Some researchers think that the human brain is not fully developed until the mid-twenties (18).
Plus, it’s only logical to reason that heavy and daily use of any psychoactive substance that temporarily alters your brain chemistry over a longer period of time, has the potential to alter your brain (chemistry) in the long-term as well.
Conclusion and How Can You Use All of This Information to Make Sure You Use Marijuana Responsibly
You’ve now got a clear idea of what the current facts are regarding the effects of marijuana on the brain.
The acute effects of marijuana on the brain relate to:
- Impairment of psychomotor and some cognitive skills like reaction time, memory, and decision making;
- Relaxation, euphoria, and sensory alteration on the positive side;
- Anxiety and paranoia on the negative side.
The scientifically backed long-term effects of marijuana include:
- Impairment of cognitive skills;
- Reduction of gray matter in the hippocampus;
- Increased risk of psychotic disorders (especially if you already have a susceptibility to psychotic illness);
- Increased risk of mood disorders.
We also conclude that all the risks related to marijuana use increase heavily when:
- You start using marijuana while young (below 18 years), and/or
- Use large doses and/or use it frequently, and/or
- You have a susceptibility towards psychotic disorders.
What are the most important tips for responsible marijuana use based on the latest scientific research?
- Don’t ever use marijuana if you’re under 18 years old;
- Unless you have a medical condition and your doctor prescribed you marijuana, re-consider why you want to use marijuana and try to see if there are alternatives that might give you similar effects, without any negative side-effects (think meditation, yoga, using CBD oil, etc.);
- Unless you have a medical condition and your doctor prescribed you daily marijuana use, don’t use marijuana daily and/or in large doses (yes this is subjective, but you get the gist);
- Don’t ever use marijuana if you’re under 18 years old, yet again, because this seems to be a very important rule;
- If you think you might be susceptible to psychotic disorders, don’t use marijuana, or find strains that contain little THC and a lot of CBD. While THC has been linked to psychotic disorders, CBD has in fact been shown to be helpful for psychotic disorders;
- Since it’s determined that it’s THC which is responsible for the psychoactive effects of marijuana, marijuana growers have been modifying their plants in a way that the THC content of their plants basically sky-rocketed. If you ask me this is not natural, so I would advise finding strains that have a more balanced THC/CBD ratio and are grown in an organic way.
If after taking into consideration what effects marijuana can have on your brain, you still want to use it, you should consider how you're going to use it.
We believe vaping marijuana is the most convenient and safest way to use marijuana. And for that, you'll need a weed vaporizer.
Marijuana smoke is harmful to your respiratory system, and vaping reduces the toxins that are found in smoke by up to 95%.
Edibles can be very tricky to dose. They can hit like a truck and are somewhat unpredictable.
If you want to experiment with CBD (which is one of the most beneficial compounds in marijuana), go to our list of recommended CBD oils.
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