Marijuanas Effects on the Human Physiology and the Brain

Marijuana is a mixture of dried, shredded flowers and leaves of the hemp plant Cannabis sativa. There are many street names for marijuana including weed, hashish, pot, reefer, boo, ace, grass, Mary-Jane, MJ, bud, the happy plant, as well as many local slang terms. All forms of marijuana have hallucinogenic properties, which come from the leaves and stems, and more importantly, from the buds or flowers of the plant. The most potent form of marijuana, hashish, comes from the resin found on the surface of the female plant.

The hallucinogenic substance in Cannabis is the chemical known as delta-9-tetrahydrocannabinol (THC).

Marijuana has many different effects on the human body. Areas effected include the brain, heart, lungs, stomach, reproductive system, immune system, and the circulatory system. Each part of the body affected has multiple ways of reacting. Cannabis use effects the user in some ways not noticeable to himself. These effects include denial, immaturity, memory loss, and delay of adolescent brain development.

Marijuana effects the brain in many different ways. Marijuana inhibits short-term memory by disrupting the nerve cells the hippocampus, the area of the brain where memories are formed. THC binding to receptors in the cerebellum slows reactions and visual tracking, impairing ability to drive or operate machinery. Long term use brings on the inability to extract and understand concepts. Deeper in the brain the psychological effects come into play. Frequent usage changes one’s perceptions, resulting in more intense physical feelings and less intense emotional feelings. Continued stimulation of THC receptors creates the need for more, resulting in addiction.

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Depending on individual physiological reactions, the use of marijuana can lead to the use of harder drugs such as heroin and methamphetamines.

A delay in adolescent brain development is common when marijuana usage begins at a young age. Basically, the teenage brain stops developing. “Some frequent users feel a lack of initiative and concern about the future, find it hard to become or stay motivated, and think things will take care of them selves.” (Wapner, Roger, 1995) As a result, the normal maturation process is interrupted. Development of coping skills, a code of ethics, acceptance of responsibility, and other signs of maturity frequently cease or regress. As a result, many milestones of life, such as graduation, may be missed.

A frequent user’s emotional development is delayed when he starts using, and usually takes much longer to develop once the user has become clean and sober for an extended period of time. Drug misuse usually leads to denial. “Denial is one of the hallmarks of chemical dependency. Frequent users not only deny that their drug use is a problem; they may begin using denial to pretend other problems do not exist either. Forgotten birthdays, missed social engagements, and unmet commitments are all ‘no big deal’.” (Wapner, Roger, 1995)

Jonathon Shedler and Jack Block (University of California, Berkeley) have done extensive studies of teenagers, which included abstainers, occasional users, and frequent users. “Frequent users are described (by family and peers) as not dependable or responsible, not productive or able to get things done, guileful and deceitful, opportunistic, unpredictable and changeable in attitudes and behavior, unable to delay gratification, rebellious and nonconforming, prone to push and stretch limits, selfindulgent, not ethically consistent, not having high aspirations, and prone to express hostile feelings directly.” (Shedler and Block, 1990)

“Frequent users are also described as critical, ungiving, not liked and accepted by others, or having much warmth and capacity for close relationships, and being just plain rude, and trying to avoid close relationships, distrustful of people, and are usually uptight and self centered.” (Shedler & Block, 1990) Finally, frequent users are described as being over-reactive to things of minor value, likely to think and associate to ideas in ways that appear unusual, and have very sensitive egos, self-defeating, concerned about the adequacy of the bodily functions, concerned about their adequacy as persons, prone to project their feelings and motives onto others, feeling cheated and victimized by life, and having fluctuating moods.” (Shedler & Block, 1990)

The heart and circulatory systems are affected by marijuana usage. The heart rate and blood pressure are nearly doubled while the user is high. People who have any type of heart disease are at an extreme risk when using any type of drug. “Cardiac injury, myocardial infarction (heart attack), or even cardiac arrest can result. Stroke brought on by excessively high blood pressure is also possible.” (Lynda Fawcett, 1998)

The lungs are affected considerably more by marijuana than tobacco since marijuana smoke is not filtered. Cannabis smoke contains approximately twice the chemicals of tobacco smoke. Inhaling any type of smoke over an extended period of time will cause cancer. Marijuana users generally inhale deeply and hold the smoke in the lungs, consequently, marijuana users develop cancer of the lungs, mouth, and throat in a significantly shorter period. Other conditions smoking causes are chronic coughs, throat and lung irritation, emphysema, and bronchitis.

“There is reasonably consistent evidence that THC can produce cellular changes such as alterations on cell metabolism, and DNA synthesis, in vitro (Bloch, 1983). There is even stronger evidence that marijuana smoke is mutagenic in vitro, and hence, that it is potentially carcinogenic for in the same reasons as tobacco smoke (Leuchtenberger, 1983).” (WHO Project on Health Implications of Cannabis Use, 1997 -Schaffer Library of Drug Policy, 1998)

“There is reasonably consistent evidence that cannabinoids impair the cell-meditated and humoral immune system in rodents. These changes have decreased resistance to infection by bacteria and viruses. There is also evidence that the noncannabinoid components of cannabis smoke impair the functioning of alveolar macrophages, the first line of the body’s defense system in the lungs (Munson and Fehr, 1983)”. (WHO Project on Health Implications of Cannabis Use, 1997 – Schaffer Library of Drug Policy, 1998)

The digestive system and appetite are affected because marijuana usage causes the “Munchies”. One is constantly hungry no matter how much is eaten. The disorientation of a marijuana high causes failure to monitor the diet, usually resulting in a weight gain. This is intensified by the lethargy (lack of energy) normal in a marijuana user. Since THC can increase appetite, as well as suppress nausea, marijuana or THC extracts are sometimes used to help counter the nausea and appetite loss caused by chemotherapy treatment for cancer and AIDS.

The reproductive system is dramatically affected by marijuana usage in both men and women. Hormone production, controlled by the brain, is disrupted. THC can destroy a number of chromosomes, resulting in cell abnormalities (mal-formed eggs and sperm, including abnormal DNA). In men, marijuana use can decrease sperm count, movement, and cause lower sex drive. Females can have egg damage, suppression of ovulation, disruption of menstrual cycles, and alteration of hormone levels. During pregnancy fetal development is slowed and neurological and physical development may be abnormal. Birth defects similar to abnormalities similar to Fetal Alcohol Syndrome – small head, irritability, poor growth and development – may be seen. Use during labor can reduce pain, but the marijuana in the mothers system can cause depressed vital signs and other stress in the baby. The baby may also be born dependent on THC.

Marijuana usage also has additional dangers for the users. Since marijuana is an illegal substance, the Food and Drug Administration (FDA) or other government agencies do not monitor the product quality. There is the possibility of a harvest contaminated by herbicides and pesticides. The marijuana may also be “cut” or “stretched” with such fillers as tobacco, lawn clippings, or manure. Suppliers can lace the marijuana with other drugs such as LSD, Angel dust, and cocaine. Any of these adulterations increase the toxicity of the marijuana, and could result in severe illness or death for the user.

Marijuana is a naturally occurring, yet toxic, plant. The effects of ingesting this plant, while temporarily pleasant, are definitely negative on all bodily systems.


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Marijuanas Effects on the Human Physiology and the Brain. (2021, Dec 24). Retrieved from

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