Dangers of recreational/medical cannabis use

According to the United Nations Office on Drugs and Crime, cannabis is the most frequently used illicit drug in the world. While cannabis is being increasingly used as a recreational drug, in addition to its medical use for the treatment of chronic pain, there is little evidence of its safety.

Some data indicate that neurocognitive functioning is adversely impacted by cannabis use, with anatomical deterioration supporting these observations. The risks are increased with the earlier age of onset.

As with any other drug, these risks should be considered alongside benefits prior to a decision on cannabis use.”

Study: Adverse Effects of Recreational and Medical Cannabis. Image Credit: OMfotovideocontent / Shutterstock.com


Cannabis sativa is the source of cannabis and its derivatives. Known by several names, such as marijuana for dried flower buds and hashish for plant resin blocks, cannabis contains multiple bioactive compounds like flavonoids, cannabinol, and cannabinoids.

Some of the most notable cannabinoids founds within cannabis include the potent psychoactive compound delta-9-tetrahydrocannabinol (THC) and anti-inflammatory cannabidiol (CBD). Both of these active ingredients act on the cannabinoid receptor 1 (CB1), with THC a partial agonist and CBD a negative allosteric modulator.

CB1 receptors are most concentrated in the central nervous system (CNS). These receptors are neurochemically similar to opioid receptors, thus influencing nociceptive pathways in the brain.

Receptor binding by cannabinoids leads to stimulation of the endogenous cannabinoid system, thereby causing endogenous cannabinoids (eCBs) to change in level, with a concomitant reduction in the release of gamma-aminobutyric acid (GABA) and glutamate. The eCBs are implicated in reward, memory, learning, and pain pathways.

In addition, CB1 and CB2 receptors may increase dopamine release while reducing the release of acetylcholine and norepinephrine.

Now that many American states have legalized cannabis, the already high rate of cannabis usage is increasing from ages as young as 16 years. Moreover, medical cannabis is becoming more common, with 40% of cancer patients using cannabis for pain management when available legally, as in Canada, Germany, and Israel.

Cannabis-based medicines (CBMs) such as dronabinol and nabiximols are also being made available. These are being used in capsule form (dronabinol) or as an oromucosal spray (nabiximols), as well as oral or inhaled solutions of generic THC. Medical cannabis is also being used instead of standard therapy for conditions like refractory epilepsy, schizophrenia, or multiple sclerosis.

All of this is taking place in the context of limited evidence that cannabis is safe. Furthermore, studies are limited by a reliance on a single source of cannabis from federal stocks, recall bias, small sample sizes, and poor external validity.

What did the study show?

An earlier Cochrane review in 2017 reports that most studies were of low to moderate quality. The use of medical cannabis could increase the proportion of people who were able to reduce their pain to half the existing level or less.

However, the global impression of any change in pain management was very low among patients, with adverse effects of cannabis use accounting for multiple withdrawals from studies on medical cannabis.

Though the frequency of serious adverse events was not found to be increased with medical cannabis as compared to placebo, the former appeared to impact the nervous system, with a higher risk of psychiatric disorders. Long-term risks have been poorly assessed. Furthermore, some authors have concluded that the cost-benefit ratio of medical cannabis is unfavorable.

Cannabis in pain relief

Among cancer patients with chronic pain, who make up 70% of patients with advanced malignancy, opioids are a first-line treatment endorsed by the World Health Organization (WHO). While high-quality studies comparing opioids and THC are lacking, it appears that nabiximols at low to medium doses provides better pain relief than placebo with adequate tolerability.

High THC doses cause sedation, whereas the THC/CBD combination provides superior analgesia as compared to either THC or placebo. In fact, this combination was maintained without the need for higher opioid medication for up to two years, while in some cases opioid dosages were reduced by 50% in patients.

Adverse effects on the CNS and gut were more frequent with oromucosal nabiximols and THC. Thus, there is an urgent need for more research to determine the optimum dosage and modes of administration.

Cognitive effects

Cannabis users tend to show defects in executive function, with poorer memory and attention than non-users. This appears to be dose-dependent and affects cognition, reward, and motivation.

Young adults with cannabis use disorder (CUD) could have cognitive impairments due to disorders of the emotional domain. This reduces normal cognitive control and decision-making capacity in emotionally strenuous situations.

Studies of brain electrical activity suggest that cannabis users have increased cortical activation at rest, perhaps because the normal inhibition of unnecessary processes that create background noise and reduce brain efficiency is impaired by cannabis.

Acute cannabis use affects working, verbal and visual memory, as well as episodic memory and attention, with higher impulsivity. In fact, small changes are detectable within a week of heavy cannabis use.

Tests of memory and learning consistently produce poorer results among cannabis users. However, these cognitive tests must account for the family background and other individual factors.

Chronic use of cannabis tends to impair memory, in addition to inducing significant brain dysfunction that affects visual-motor pathways. If chronic users who abstained for an average of 15 hours are compared with chronic tobacco users, the former were shown to have worse learning and recall memory, with more interference and greater forgetfulness. Reaction times were also longer among chronic cannabis users, particularly when sustained attention was required.

Interestingly, as compared to heavy use, cannabis use for three or fewer days a week was found to improve all-round health, with better appetite and depression that was comparable to those who quit cannabis altogether. Even so, improved cognition was associated only with previous cannabis users.

A similar reversion of memory was found with the use of an adenosine A2A receptor (A2AR) antagonist in chronic users, perhaps because it enhanced synaptic plasticity in the hippocampus from its depressed state.

Structural effects

Neuroimaging has shown the occurrence of abnormalities in the volume and gray matter density of the hippocampus among cannabis users. White matter is also implicated, as it is a dense site for CB1 receptors.

The association of poor working memory, a brain function that develops mostly in adolescence, occurs more significantly in frequent adolescent cannabis users as compared to adults. This is reflected in impaired activation of posterior parietal cortical areas and increased activation of other parts of the prefrontal cortex.

The former may indicate a risk factor for cannabis use since it did not show any difference between single- and repeated-use cases. Conversely, cannabis users exhibit neurological changes that indicate an adaptive process, wherein they use relatively inefficient strategies to achieve comparable results as non-users.

Cannabis may reduce the aesthetic pleasure of listening to music through reward pathways in the brain. This was compensated for by adding CBD to the drug.

Cannabis use prior to the onset of schizophrenia is associated with atrophy of neural gray cells, but not in patients with either schizophrenia or bipolar disorder who were using the drug after their diagnosis. There is some evidence that adolescent cannabis use can prevent or improve neural impairment in psychotic patients; however, this must be further studied.

Is cannabis carcinogenic?

Patients with throat cancer are more likely to use cannabis, but not those with other head and neck cancers. These patients were also more likely to have chemoradiation than surgery alone. Cannabis smoking produces toxins that can produce cancer of the head and neck, as well as immunosuppressants and mutagens.

One earlier study indicated a threefold risk of head and neck cancer with cannabis use, especially in those below 55 years of age. However, this has not been confirmed.

Biological plausibility exists since cannabis upregulates the epidermal growth factor receptor (EGFR) and its downstream elements, which are found at higher levels in most squamous cell cancers of the head and neck.

Cannabis smoking also alters the oral microbiome in the throat and lateral edge of the tongue, which is where most of these cancers occur.

Is cannabis addictive?

Addiction is described by different models, of which the three-stage model appears to fit CUD. This involves the basal ganglia, which supplies the feeling of intoxication; the amygdala, which drives negative feelings during withdrawal; and the prefrontal cortex, which is responsible for preoccupation with or anticipation of the next dose. Cerebellar CB receptors may also be involved.

About 10% of cannabis ever-users show CUD, with over half of this being attributable to genetic effects. Importantly, the prevalence of CUD increases over time, as more young individuals between the ages of 12 and 17 years begin using cannabis as compared to young adults up to 25 years. This makes it important to recognize risk factors for this condition.

Chronic cannabis use may permanently alter cognition by changing brain processing in pathways like the prefrontal-limbic system network. Abstinence for over one month was not associated with a better response to emotional stimuli in chronic users with dependence. 

These results suggest that chronic cannabis use may result in addictive changes that cause persistent modifications in emotional processing.”

This effect appears to be marked by a shift from the reduced coupling of the medial orbitofrontal cortex (mOFC) with the dorsal striatum to improved coupling, which may reflect the beginning of dependence. Moreover, this switch from ventral to dorsal striatal coupling with the prefrontal cortex could explain how voluntary drug intake switches to habitual intake, or dependence, by impaired inhibition of the impulse.


The current review calls for much larger trials with stringent quality standards to produce results with external validity. This research is urgently needed, as recreational and medical cannabis is being legalized in many societies, particularly the United States, where dozens of states have taken such measures.  

Thus, it has become imperative to improve current understanding of both the basic science and clinical applications of cannabis.”

Journal reference:
Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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  1. Duncan Wallace Duncan Wallace United States says:

    I hope you don't expect anyone to come running to save you from the wolf. You and your friends keep crying wolf and when we investigate your claims they're just not true. Grow up.

  2. Michael Carey Michael Carey Lithuania says:

    Since 1996, California's (and other states later laws) had legal medical cannabis, and since then, many tens of millions of Americans (and Canadians) have been using medical cannabis under medical supervision for more than 25 years, and no real epidemics or raises in the rates of schizophrenia or cancer has been occurring due to cannabis use.
    Add the many other millions regularly using cannabis through state legalization, and still, no increases in disease or death resulting from cannabis use.

    But, further studies are required to determine the EFFICACY (as it's now known to be GRAS) of cannabis as medicine should be done. 'Cuz 100 million people using cannabis will little ill effect just isn't convincing.

  3. Daniel Patrick McAteer Daniel Patrick McAteer United States says:

    What a bunch of BS, idiots like you are why it still hasn't been federally legalized. You want to do a smear piece on a dangerous drug, how about alcohol, I wonder how many have died from drunk driving????

  4. andrew lendvay andrew lendvay United States says:

    I can say something you think is really smart or I can tell you the truth. The psychological effects of cannabis are negligible and don't really matter in this full active mind control field. The radio waves they're shooting into our heads are overwhelmingly psychoactive and fully mind-controlling. All you're likely to get with cannabis use is a little euphoria...Chemicals can still be and appear to be mind-altering because chemicals give rise to the electrical activity in the brain. But this doesn't change the fact that the mind per se is entirely electrical and totally plastered! Blitzed!

  5. Dragoljub Mitrovic Dragoljub Mitrovic United States says:

    And that's not including lung tar buildup and cardio vascular damage from all the carbon monoxide.  Oxidative stress and premature ageing.

  6. Joshua Petteys Joshua Petteys United States says:

    I'm no scientist but I do believe that lack of evidence is in itself not evidence. Lack of evidence on it's safety? I can do that to, watch this... Lack of evidence on it's dangers. I can't believe with Alcohol, Tobacco, Cocaine, Heroin, Fentanyl, ect. that you waste your time writing a garbage report on Marijuana LMAO. And your an OBGYN? How the hell is that remotely connected? As an Aviation Mechanic I to love to write reports on proper Bridge Engineering LMAO.

  7. Monica Eaglespirit Monica Eaglespirit United States says:

    I recall since the 60s, how reefer madness, a  movie payed by corporations that could lose money if it was proven safe. As the preposterous lie, showing one hit could cause insanity and murderous behavior. And users were depicted as scummy mentally deranged criminals and seedy individuals .
      The drug companies are projected to lose over a trillion dollars of profits by end of year. Besides them, the tobacco industry is also experiencing massive customers loss. Paper, Criminal justice industry also find of the effect of calming Cannibis. I've fought this lies and crap, claiming more studies need be done but the evidence they claim was proven false and political propaganda during President Carter in the 70s. I can quote comprehensive studies after studies that prove the benefits of medical pot saving lives and ending needless suffering.  Infact,  a now kept secret medial Cannibis program federally established, still in operation today from the 1970s. Clients of the program get cans of the best joints federal tax dollars can make. But who sponsors the doctors and more in publishing these false conclusions already proven wrong and politically motivated by lobbyists money,  repeatedly over a 100 year period. ?
    Don't trust a company that's drugs side effects cause diabetes, cancer, and more while pots side effects are mostly the munchies and concern towards others. I learned a new one you have to hear. Drug companies are infiltrating the medical marijuana dispensaries and destroying the usefulness of cannabis by lowering THC-9 levels. This is resulting in patients turning back to Drug companies and poisoning them with medication hurtful and not effective. Consider the source please and check potency. You should not need to take more then a few hits for strong effects but Columbia care and many products they sell, I've tested and proved there potency has dropped from tests of 4 years ago by more than 68%. Vape pens less then 4%. Down from 50 to 90%. I've informed them that if they don't fix this, they will be called out and findings made public. There is a fight for safe medicines for us and if we don't stand up to protect the truth, patients will suffer and die. No exaggeration! Villafing medical and recreational marijuana has been going on since the bigots of society powered by racist hate towards blacks and Hispanics challenging the rights to sit in the front of a bus while facing even death to be treated as equal. Pot sometimes was scapegoat as the problem, wrongly so. STOP THE DRUG AND TOBACCO COMPANY LIES. Pot is an herb that is safer then anything the drug and tobacco companies supply. How long is the side effects mentioning during the commercial that sells them? Answer that. M.Z. retired ceo of mental health and disability advocate, VOICES OF INDEPENDENCE AND CONSUMER EMPOWERMENT INC  I've been shot at supporting patients and other civil rights.  Peace ✌️

  8. Takes Direction Takes Direction United States says:

    52 years using, 20 years medical, I smoke 1.5 gms+ most days
    Forgot what I wanted to post...     /s

  9. andrew lendvay andrew lendvay United States says:

    They.deleted mine because it was the truth. This is what I said, let people decide for themselves, let this be a democracy!..I can say something you think is real smart or I can tell the truth. I forget!!!!!! The psychological effects of cannabis use are negligible and don't really matter in this full active mind control field. The radio waves they're shooting into our heads are overwhelmingly psychoactive and fully mind controlling. All cannabis use is likely to do is give you feelings of euphoria. ..chemicals can still appear to affect the mind because chemicals give rise to the electrical activity in the brain known as the mind! Nevertheless, this doesn't change the fact that the mind per se is entirety electrical and totally plastered!! Blitzed!!

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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