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Strange Side Effects of Marijuana, Says Science

According to medical experts, the following side effects can happen when smoking marijuana.

Whether used for recreational or medical purposes, smoking marijuana can offer benefits such as reducing anxiety, inflammation, nausea and vomiting caused by cancer chemotherapy, among other things. However, some people can experience unusual and unwanted side effects that aren't fun to deal with. Dr. Keith Heinzerling, MD, internist and addiction medicine specialist at Providence Saint John's Health Center in Santa Monica, CA says, "The effects of marijuana on the brain depends in part on the 'strain' of marijuana and whether the person is a chronic user or not." Eat This, Not That! Health talked to medical experts who explained 9 strange side effects that can happen when smoking marijuana. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.


Marijuana and Your Brain

Brain impulses, thinking process

According to Dr. Heinzerling, "Marijuana contains a large number of natural compounds that may affect the brain but THC and cannabidiol (CBD) are the two best characterized. THC is responsible for most of the psychoactive effects associated with marijuana use including the high as well as increased appetite ('munchies'), but also negative effects such as risk of addiction, anxiety or panic attacks, and psychosis. THC acts through cannabinoid receptors in the brain and body which are the receptors for endogenous cannabinoid neurotransmitters that are naturally found in our brains and bodies. CBD is not psychoactive and may counteract some of the potential negative effects of THC, and may have anti-anxiety effects. Also a pharmaceutical version of CBD was recently approved by the FDA to treat certain types of epilepsy.

The pharmacologic effects of marijuana in the brain acutely seem to be primarily the results of THC acting via cannabinoid receptors called CB1 and CB2 which then effect multiple other neurotransmitter systems including dopamine, serotonin, glutamate, GABA, noradrenaline, and acetylcholine. Dopamine is involved in addiction and psychosis and increases in dopamine as a result of THC contributes to the potential for addiction and psychosis with marijuana use. Effects of THC on acetylcholine are thought to be involved in impairments in cognition and coordination that occur with acute marijuana intoxication and make driving under the influence of marijuana dangerous.

Selective breeding of marijuana that is very high in THC content and low in CBD and the use of extracts that are enriched in THC increases the risk of bad effects from marijuana use."

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Cyclical Vomiting Syndrome

young woman with nausea in all denim outfit sitting on bed
Shutterstock / New Africa

Dr. Taylor Graber, an MD Anesthesiologist and owner of ASAP IVs explains, "Also known as cannabinoid hyperemesis syndrome, this is a known phenomenon where individuals who chronically use marijuana experience repeated and severe bouts of vomiting and abdominal pain. It is rare and usually only occurs with heavy/daily marijuana users. Interestly, as a short term therapy, marijuana can help with acute episodes of nausea, but as a chronic/daily ingestion, it can predispose individuals to severe nausea episodes. These frequently require invasive medical treatment in the form of IV therapy (whether in the home or in the emergency department) to help stop the nausea with medications and replace needed fluids with saline."

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Pharmacologic Resistance

physician medicine doctor or pharmacist sitting at worktable, holding jar of pills in hands and writing prescription on special form.

Dr. Graber says, "Chronic Marijuana use can lead to a physiologic resistance to many pharmaceuticals, including opioids, local anesthetics, general anesthetics, and others. This has been an area of increasing research, but it is a known phenomenon, and I can speak from first hand experience, that patients who frequently use marijuana (either through edibles or through inhalation) have a higher requirement of medications to induce anesthesia (go to sleep for a procedure) or maintain anesthesia (stay asleep for a procedure). They also have a much higher tolerance for opioids, meaning that it often requires more medication to treat acute pain than similar patients who do not use marijuana. I have frequently been surprised by how much these limits are increased, with drug doses 2-4x the amount needed for similar patients. This doesn't apply only to surgery, but can apply to outpatient treatment of pain or hospitalizations as well."

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Sexual Dysfunction

worried senior man in tension at bed.

"While not the most common symptom, there is some evidence supporting that those who suffer from marijuana abuse have experienced sexual dysfunction incuding erectile dysfunction and issues with reaching orgasm," Dr. Abe Malkin, Elite Home Detox states. "Smoking tobacco restricts blood flow to the veins and arteries, and a person who smokes cigarettes has an increased risk of developing ED. Smoking marijuana, particularly in conjunction with tobacco, carries a similar risk. Cannabinoid receptors are present in the smooth muscle tissue of the penis. Because marijuana inhibits regular bodily functions, it may make it harder for a person to get an erection.  A 2019 study from the American Journal of Men's Health of over three thousand healthy men revealed that ED was twice as high in frequent cannabis users as it was in control groups."

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Lung Infections

Attentive doctor analyzing x ray of his patient

Dr. Malkin explains, "Smoking marijuana hurts the lungs' first line of defense against lung infection by attacking the cells that help remove dust and germs, as well as causing more mucus to be formed. Marijuana use also suppresses the immune system which allows the body to clear infections. Studies show that this leads to an increased risk of lower respiratory infections  According to the American Lung Association, regular marijuana use leads to chronic bronchitis and can cause an immune-compromised person to be more susceptible to lung infections. I want to mention that this also includes the use of vape pens(inhaling cannabis concentrates or liquids) and dabbing (inhaling vaporized cannabis concentrates.) Smoking marijuana has also been linked to cases of air pockets in between both lungs and between the lungs and the chest wall, as well as large air bubbles in the lungs among young to middle-aged adults, mostly chronic smokers of marijuana."

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Impaired Vision

ophthalmologist checking eyesight, showing letters on chart, focused vision

Yuna Rapoport, MD, MPH Board Certified Ophthalmologist says smoking marijuana can "decrease night vision by affecting the retinal ganglion cells. These cells take visual input and transform light into electrical pulses in the brain. This signaling is decreased with marijuana, thus causing fewer signals to reach the brain. In addition, smoking marijuana can lower the intraocular pressure (the pressure inside your eye) by about 25% Some people think this is a great way to treat glaucoma (the treatment for which is to lower the pressure, but to maintain the reduction you would need, you would have to ingest about 18-20mg of THC 6-8 times a day – which is usually impossible for most people." 


Slower Perception of Time

Woman check her watch.

Holly Schiff, Psy.D. Licensed Clinical Psychologist says, "One side effect is having a slower perception of time, also why sometimes smoking weed is a relaxing experience for most because it forces you to slow down. This can be due to altered blood flow to the cerebellum, which is linked to our body's timing system. Users experience time dilation, where they tend to overestimate the amount of time that has actually passed. Cannabis acts on receptors in the thalamus, which regulates our perception and sensation. Cannabis interferes with our sensory input filtering system and changes the filter that controls how you perceive time."


Laughing and Giggling

Group of Friends Laughing

According to  Schiff, "Marijuana activates blood flow to the right frontal and left temporal lobes of the brain, which are both associated with laughter. Cannabis puts you in an altered state, which makes the reflex to laugh more likely to be triggered. It also boosts levels of dopamine, which is a chemical that can also trigger the laugh reflex – making unfunny things funny to you in that current state. It also acts on the frontal lobe, which is responsible for inhibiting behavior, so typically you might deem giggling inappropriate in certain situations, but while high, your inhibition is lowered and you are more likely to laugh. Dopamine and serotonin release also lower impulse control."


Increased Appetite


"One side effect of smoking marijuana is increased appetite, or what is commonly referred to as the munchies," Schiff states. This seems to be due to an increase in the hormone that the stomach releases when it is empty, which tells the brain that it needs to look for food. There are also neurons in the hypothalamus that control appetite stimulation which are activated when cannabis is used.


Dry Mouth

Woman with mirror

Dr. Malkin, explains, "Dry mouth or cottonmouth (medically called xerostomia) is another frequent side effect of cannabis abuse. The cannabinoid receptors are located in the brain – CB1 and CB2 – and also in the submandibular glands found beneath the bottom of the mouth. These glands produce nearly three-quarters of our body's saliva. When THC binds to these receptor sites both in the brain and in these glands, the glands stop receiving messages from the peripheral nervous system- specifically the parasympathetic nervous system- to produce saliva. Thus, there is a reduction in the amount of saliva produced resulting in the feeling that your mouth is dry." And to get through this pandemic at your healthiest, don't miss these 35 Places You're Most Likely to Catch COVID.

Heather Newgen
Heather Newgen has two decades of experience reporting and writing about health, fitness, entertainment and travel. Heather currently freelances for several publications. Read more about Heather