The Human Body:  Brain & Lungs & Heart

Articles & More Research on Physical Health Effects

  1. Marijuana over-activates the endocannabinoid system (neural communication network), causing the high and other effects that users experience. These include distorted perceptions, paranoia, reduced motor skills, decreased reaction time, difficulty with thinking and problem solving, and disrupted learning and memory.  These effects can last up to 28 days after abstinence from use.  
  2. Marijuana smoke is an irritant to the lungs. Research has shown marijuana smoke contains 50-70 percent more carcinogenic hydrocarbons than does tobacco smoke, as reported by the American Lung Association. These are irritants to the lungs, resulting in greater prevalence of bronchitis, cough and phlegm production. Marijuana smokers are actually exposed to more of these chemicals per puff than tobacco smokers because tobacco cigarettes typically have filters through which smokers inhale, whereas marijuana joints do not. Also, marijuana smokers tend to inhale and hold the smoke in their lungs longer than cigarette smokers.
  3. Marijuana raises heart rate by 20-100 percent shortly after smoking. This effect can last up to 3 hours. In one study, it was estimated that marijuana users have a 4.8 increase in the risk of heart attack in the first hour after smoking the drug.
  4. Brain imaging of regular use of marijuana shows a smaller hippocampus which is responsible for memory formation, sleep regulation, and regulating stress responses. The hippocampus develops throughout  adolescence, and is one of the few areas in the brain where new brain cells are generated throughout our lives.  Scientists have found that THC dampens down the activity of hippocampal neurons, below the level needed to trigger the formation of a memory.
  5. Smoked marijuana bypasses the body’s natural protective systems: first pass metabolism of the liver and the absorptivity going through the stomach or the gut lining.
  6. Marijuana use affects nearly every organ system in the body. It can have a profound impact on people’s education, employment, and personal life.
  7. Marijuana decreases sleep quality, which in turn affects overall quality of life by contributing to memory impairment, unpleasant moods, immune system impairment, and a host of other significant deficits. 
  8. THC makes it harder for the body to fight infection and disease.
  9. Within a few minutes after inhaling marijuana smoke, an individual's heart rate speeds up, the bronchial passages relax and become enlarged, and blood vessels in    the eyes expand, making the eyes look red.  
  10. Smoking three cannabis joints will cause you to inhale the same amount of toxic chemicals as a whole packet of cigarettes, according to research published in France. Cannabis smoke contains times seven more tar and carbon monoxide, the French National Consumers’ Institute concluded. The institute tested regular Marlboro cigarettes alongside 280 specially rolled joints of cannabis leaves and resin in an artificial smoking machine.
  11. There are no circumstances in which they may be useful” .This is partly due to the increasing cardiac frequency and alterations to motor performance that marijuana produces.  In particular, marijuana is known to increase heart rate while decreasing cardiac stroke volume, resulting in diminished peak performance....

Tetrault, J.M., et al. Effects of cannabis smoking on pulmonary function and respiratory complications: a systematic review. Arch Intern Med 167, 221-228 (2007).
Hoffman, D.; Brunnemann, K.D.; Gori, G.B.; and Wynder, E.E.L. On the carcinogenicity of marijuana smoke. In: V.C. Runeckles, ed., Recent Advances in Phytochemistry. New York: Plenum, 1975.