The fact is, no one can say what definite effect months or years of cannabis use has on the brain, as there just isn’t enough research out there to say for sure. Moreover, the human brain (or indeed any type of brain) is incredibly complex, and there are all sorts of stimuli that will affect its development over the course of its life. Whether or not a person uses marijuana is just one small piece of the puzzle.
Marijuana definitely has an effect on the brain in the short-term, but determining the long-term effects of regular consumption will be difficult to tell, especially as it’s still federally illegal and therefore difficult to study properly. When we mention the “developing brain”, most people think of the teenage years. Yet, in reality, the brain is in constant development, and can be roughly broken down into five main ages. We shall use these five ages to break down marijuana’s effects on the brain throughout all the brain’s development stages …
The brain develops within 3 weeks of conception. In the third week, the neural plate is formed, and by the fourth week the neural plate widens to form the cephalic (the concentration of nervous tissue) end that forms the head of the baby. By the fifth week, the basic structure of fore, mid and hindbrain is developed. By 9 months, the baby has 100 billion brain cells and millions of support cells.
We know that alcohol and tobacco use during pregnancy has a negative effect on prenatal brain development. But what about exposure to cannabis? Marijuana use during pregnancy shows weak links between fetal cannabis exposure and congenital anomalies or preterm delivery. There is no evidence that cannabis has similar effects as fetal alcohol syndrome, although there have been some reports. Cannabis use does not seem to be associated with low birth weight or preterm birth.
However, this is not to say there aren’t any negatives to cannabis use whilst pregnant. Cannabis exposure affects fetal growth trajectories, learning development and memory impairment in exposed offspring. Post-birth, studies so far show that there is some correlation between neonatal marijuana exposure and behavior. Prenatal marijuana exposure was associated with increased tremors and startles, and poorer habituation to visual stimuli.
Though there aren’t a huge number of studies on prenatal cannabis exposure, it is fair to say that so far the evidence shows that cannabis use during pregnancy is negative. However, the research mostly focuses on THC and generalized cannabis use, not non-psychoactive cannabinoids like cannabidiol (CBD). In fact, CBD may be helpful to help ease the pain and stress of childbirth, and studies on mice have shown no effects with regards to prenatal CBD exposure.
This is when the human brain is at its most “plastic” and flexible. Though learning, memory and language begin before we are born, this is when connections are made and broken fastest. Though there aren’t huge numbers of studies on exposure to marijuana during childhood and its effects, it does seem that marijuana metabolites can be found in children exposed to marijuana smoke. The precise effects secondhand marijuana smoke has on children is not yet known, but some doctors and scientists believe that exposing children to secondhand marijuana smoke is generally best avoided.
However, when it comes to cannabis and children, we have a tendency to be a little “typical minded”. What about all those sick kids – the ones suffering from cancer, autism or epilepsy? The fact is, we give sick children immensely harmful medications like antipsychotics without considering their long-term effects, whereas cannabis could well be a much safer alternative. Why do we not look at the brain changes caused by prescription medications in children as well as cannabis? (Well, we do, but it’s not reported in the media all too often.)
Whilst it could easily be argued that cannabis isn’t ideal for children, this isn’t to say that it doesn’t have its place as a potentially very effective pediatric medicine. Yes, there are elements of the cannabis plant that could potentially be somewhat “neurotoxic” to children, but there are are huge therapeutic opportunities, too – ones that we really ought not to avoid. Longitudinal studies are also needed in order to see how having consistent cannabinoid concentrations affect children using cannabis for medical purposes.
This is the age people most often think of when they say “cannabis isn’t good for the developing brain.” Why the focus on the teenage years, though? Perhaps it’s because that’s when many people experiment with cannabis. There is also the image of a slightly malcontent youth who finds solace among a peer group of “alternatively-minded” people who use cannabis – an image that has some validity for many people, we might say! There’s also the hormones, and the fact that myelination and “synaptic pruning” start occurring during the teenage years
However, the effects of cannabis on the adolescent brain are not entirely known, and there are all sorts of mixed results. For example, for those suffering from Attention-Deficit Hyperactivity Disorder (ADHD), early initiation of cannabis use was linked with poor cognitive outcomes when patients were under 16. However, for ADHD sufferers who started to use cannabis regularly after the age of 16, marijuana did not aggravate long standing cognitive defects. There is also no known association between IQ loss and adolescent cannabis use.
As it stands, marijuana is the most commonly used illicit drug used by adolescents. Adolescence is also the time when CB1 receptors are said to proliferate in the human brain, and disturbing this pattern with cannabis use may have deleterious effects. Early cannabis use by young teenagers may have neurodevelopmental effects, but later use by older teenagers/young adults may have less problematic effects. This is because CB1 receptors are fully formed, and excess neurons are trimmed down. For this reason, it is perhaps best for anyone under the age of 21 who doesn’t need marijuana for medical reasons to avoid it! The age restrictions as they stand may be a little rough and arbitrary, but could be useful.
This is when you’ll be stuck with your brain for quite some time. Or, so it is easy to think. Apparently, the peak of our brain’s powers come at the age of 22, and lasts until the late 20s/early 30s, when cognitive decline starts to settle in. This is where marijuana science starts to get interesting.
Where cannabis may debilitate brain development in the young, it might actually be an aid for brain development! This is a process known as “neurogenesis” (aka “hippocampal neurogenesis”), meaning the growing of new brain cells. How does this work? Well, the theory is that flooding the brain with phytocannabinoids prevents synapses from being lost, and can even help develop new synapses in the brain to develop in order to “catch” all the phytocannabinoids. Research so far suggests that cannabis can help the proliferation – but not differentiation – of neurons in the brain. Hippocampal neurogenesis produces anxiolytic- and antidepressant- like effects.
So yes, this means that, if one were to start using cannabis, it is best to do it in adulthood, preferably after the age of 21. This is when people are most likely to get the most advantage of marijuana for wellness at this age. There is also no evidence to suggest that daily marijuana use amongst adults causes brain abnormalities.
This is arguably when cannabis has most therapeutic use for people. This is the age when most people start to develop illnesses and diseases. Arthritis, glaucoma and various neurodegenerative diseases are more commonplace in old age, as are the chances of developing cancer and various other conditions.
At this stage in life, people start to lose brain cells in areas like the hippocampus – the area where memories are stored. This is one of the reasons why so many people start to forget names and plenty of other things when they start to get older. Also, as we’ve mentioned above under “Adulthood”, marijuana can help promote neurogenesis, and therefore can maybe even halt memory loss. Recent studies on older mice suggest that low-doses of THC boosts memory and learning.
The implications of this are huge, as it means that cannabis may help stave off dementia and prevent memory loss in those suffering from Parkinson’s disease. CBD may also have anti-inflammatory, antioxidant and neuroprotective effects, making it an excellent medication for stroke/traumatic brain injury victims. The neuroprotective abilities of CBD also makes cannabis great for other degenerative diseases like multiple sclerosis (MS) and the like as well. Moreover, the fact that cannabis can be used for many conditions (arthritis, depression and lots more) means that it can be used to reduce or replace lots of other pills that have nasty side-effects.
Though there is no definitive evidence suggesting that cannabis affects brain development, it is fair to say with the evidence we do have that whether or not cannabis affects the brain’s development depends on the age of the user. For young people under the age of 18/21, non-medical use may be best avoided, whereas for those aged over 21, getting themselves a medical marijuana card could very well be a benefit to one’s health and wellness.
There also needs to be more study on how specific cannabinoids help or hinder the brain, and many of the studies that look at marijuana’s effect on the developing brain forget to control for tobacco, alcohol and drug use whether licit or illicit. This can have huge impacts on the studies, and may sometimes lead us to erroneous conclusions. In the meantime, we will say that, for most adults, cannabis will not likely cause massive changes in the brain. For children and adolescents, this could be very different.