The Negative Health Effects of Marijuana

man smoking marijuana

Paul Edmondson Collection / The Image Bank / Getty Images

Although legalization activists and many marijuana users believe smoking pot has no negative effects, scientific research indicates that marijuana use can cause many different health problems.

Marijuana is one of the most commonly used illicit drug in the United States. When smoked, it begins to affect users almost immediately and can last for one to three hours. When it is eaten in food, such as baked in brownies and cookies, the effects take longer to begin, but usually last longer.

Short-Term Effects

The short-term effects of marijuana include:

  • Distorted perception (sights, sounds, time, touch)
  • Problems with memory and learning
  • Loss of coordination
  • Trouble with thinking and problem-solving
  • Increased heart rate

Sometimes marijuana use can also produce anxiety, fear, distrust, or panic.

Effects on the Brain

The active ingredient in marijuana, delta-9 tetrahydrocannabinol or THC, acts on cannabinoid receptors on nerve cells and influences the activity of those cells. Some brain areas have many cannabinoid receptors, but other areas of the brain have few or none at all. Many cannabinoid receptors are found in the parts of the brain that influence pleasure, memory, thought, concentration, sensory and time perception, and coordinated movement.

When high doses of marijuana are used, usually when eaten in food rather than smoked, users can experience the following symptoms:

Effects on the Heart

Within a few minutes after smoking marijuana, the heart begins beating more rapidly and the blood pressure drops. Marijuana can cause the heartbeat to increase by 20 to 100% and blood pressure is slightly reduced.

According to a review published in 2017, marijuana users' risk for a heart attack ranges from four to five times higher within the first hour after smoking marijuana, compared to their general risk of heart attack when not smoking.

Effects on Your Bones

Research published in 2017 found that people who smoke large amounts of marijuana on a regular basis have reduced bone density, which can increase the risk of bone fractures.

The study at the University of Edinburgh used DEXA-scan x-rays and found that heavy users of marijuana had a lower body weight and a reduced body mass index (BMI), which could contribute to loss of bone density. Heavy users were defined as those who had smoked more than 5,000 times during their lifetime.

However, another study published in 2017, looked at survey and health information for almost 5,000 adults and didn't find any association between decreased bone density and marijuana use.

Effects on the Lungs

Smoking marijuana, even infrequently, can cause burning and stinging of the mouth and throat, and cause heavy coughing. According to a review published in 2019. scientists have found that regular marijuana smokers can experience the same respiratory problems as tobacco smokers do, including:

  • Daily cough and phlegm production
  • More frequent acute chest illnesses
  • Increased risk of lung infections

Most marijuana smokers consume a lot less cannabis than cigarette smokers consume tobacco, however, the harmful effects of smoking marijuana should not be ignored. Marijuana contains a similar amount of carcinogenic hydrocarbons as tobacco smoke and because marijuana smokers typically inhale deeper and hold the smoke in their lungs longer than tobacco smokers, their lungs are exposed to those carcinogenic properties longer, when smoking.

What About Cancer?

According to a review published in 2015, one study found that marijuana smokers were three times more likely to develop cancer of the head or neck than non-smokers, but that study could not be confirmed by further analysis.

Because marijuana smoke contains three times the amount of tar found in tobacco smoke and a number of carcinogens, it would seem logical to deduce that there is an increased risk of lung cancer for marijuana smokers. However, researchers have not been able to definitively prove such a link because their studies have not been able to adjust for tobacco smoking and other factors that might also increase the risk.

Studies linking marijuana smoking to lung cancer have also been limited by selection bias and small sample size. For example, the participants in those studies may have been too young to have developed lung cancer yet. Even though researchers have yet to "prove" a link between smoking pot and lung cancer, regular smokers may want to consider the risk.

Effects of Exposure During Pregnancy

Several studies have found that children born to mothers who used marijuana during pregnancy exhibit some problems with neurological development. According to a 2018 review of those studies, prenatal marijuana exposure can cause:

  • Altered responses to visual stimuli
  • Increased tremulousness
  • Problems with sustained attention and memory
  • Poor problem-solving skills
Was this page helpful?

Article Sources

  1. National Institute on Drug Abuse. Most Commonly Used Addictive Drugs.


  2. National Institute on Drug Abuse. Marijuana.

  3. Noble MJ, Hedberg K, Hendrickson RG. Acute cannabis toxicity. Clin Toxicol (Phila). 2019;57(8):735-742. doi:10.1080/15563650.2018.1548708

  4. Goyal H, Awad HH, Ghali JK. Role of cannabis in cardiovascular disordersJ Thorac Dis. 2017;9(7):2079–2092. doi:10.21037/jtd.2017.06.104

  5. Sophocleous A, Robertson R, Ferreira NB, Mckenzie J, Fraser WD, Ralston SH. Heavy Cannabis Use Is Associated With Low Bone Mineral Density and an Increased Risk of Fractures. Am J Med. 2017;130(2):214-221. doi:10.1016/j.amjmed.2016.07.034

  6. Bourne D, Plinke W, Hooker ER, Nielson CM. Cannabis use and bone mineral density: NHANES 2007-2010. Arch Osteoporos. 2017;12(1):29. doi:10.1007/s11657-017-0320-9

  7. Tashkin DP, Roth MD. Pulmonary effects of inhaled cannabis smoke. Am J Drug Alcohol Abuse. 2019;:1-14. doi:10.1080/00952990.2019.1627366

  8. Huang YH, Zhang ZF, Tashkin DP, Feng B, Straif K, Hashibe M. An epidemiologic review of marijuana and cancer: an update. Cancer Epidemiol Biomarkers Prev. 2015;24(1):15–31. doi:10.1158/1055-9965.EPI-14-1026

  9. Hasin DS. US Epidemiology of Cannabis Use and Associated Problems. Neuropsychopharmacology. 2018;43(1):195–212. doi:10.1038/npp.2017.198