Marijuana Research: What Are the Long-Term Effects of Heavy Marijuana Usage?

image of a person completing a puzzle of a brain and there is only one piece missing to show the possible long-term effects of marijuana

Marijuana usage can be a controversial and divisive issue; its consumption, effects, moral consequences, and legal standing can be complicated, and as new laws and new information continue to sweep the nation, it may be difficult to separate fact from fiction. Luckily, on topics like the effects of long-term marijuana use, we can look toward scientific and psychological studies to ascertain the truth about just how marijuana will affect you over time. While marijuana has some positive medical uses, and the research for benefits of cannabis is continuing, most of the effects of early, long-term marijuana usage appear to be negative.

Cognitive Developments: Learning, Memory, and Education 

According to the National Institute on Drug Abuse, marijuana affects brain development, especially when use begins in the teenage years. When the drug is present while the brain is still trying to grow, the brain may have issues making connections, impairing things like thinking, learning, attention, and memory. These affects are certainly long-term, and researchers also believe that even after quitting, brain functions are still lacking.

A Duke University study found that "people who started smoking marijuana heavily in their teens and had an ongoing marijuana use disorder lost an average of 8 IQ points between ages 13 and 38. The lost mental abilities didn’t fully return in those who quit marijuana as adults."

Many researchers use IQ tests and other cognitive tests to gauge the long-term effects of marijuana, and the evidence is fairly overwhelming that frequent users have cognitive impairments compared to non-users. The brain development problems coupled with lower cognitive scoring can lead to poor results in education, such as lower grades, failures, or even drop-outs.

Education can also be affected by memory impairments. Specific research has been done on marijuana and memory, as cannabis affects the hippocampus, the brain's short-term memory center. American Addiction Centers reports that people who smoked weed regularly as teens often have memory problems as adults, including false memories and poor long-term storage, even abnormally shaped hippocampal regions in the brain.image of the brain with tons of lines connecting to other parts of the brain and just outside of the outline of the brain

Satisfaction and Achievement 

On a similar note, "Adverse Health Effects of Marijuana Use" also points to decreased levels of overall satisfaction and achievement for marijuana users. The above impairments and academic roadblocks play into this, but there is evidence that "heavy marijuana use has been linked to lower income, greater need for socioeconomic assistance, unemployment, criminal behavior, and lower satisfaction with life."

Marijuana is also known to negatively affect relationships, from the personal to the professional. When the hobby becomes a habit, it can be difficult to focus and hard to make time for the people around you. For some, weed becomes a priority over people, and this can be very detrimental to social developments and may lead to missed opportunities, lack of motivation, and an overall poor sense of well-being.

Marijuana use also generally amplifies risk factors; sensory and judgement impairment can increase the chance of negative situations like hospitalizations or car accidents, leading to a wide array of potential consequences if not used responsibly. DUIs, for example, are a serious concern, especially in regions where marijuana has been recreationally legalized. The article referenced above reports that: "According to a meta-analysis, the overall risk of involvement in an accident increases by a factor of about 2 when a person drives soon after using marijuana."


Perhaps contrary to popular belief, marijuana can be an addictive substance. Long-term and frequent use can certainly lead to substance abuse and addiction. The National Institute on Drug Abuse states that between nine and 30 percent of marijuana users develop a use disorder like addiction, and for those who start use before the age of 18, the likelihood of a use disorder increases up to seven times that.

Regular users trying to cut themselves off may experience addiction symptoms like cravings, anxiety, loss of appetite, insomnia, or altered moods. There are currently no medications or treatments to help those recovering from a marijuana use disorder, but therapy and incentives can help.

Heart and Lung Conditions3D rendering of heart and lungs in the body

Some people think of cigarette smoking and marijuana smoking as having very different effects and consequences. However, smoking weed can have similar negative effects to smoking tobacco. The smoke and toxic chemicals can cause bronchial and lung issues, leading to coughs, trouble breathing, mucus, and more.

Breathing in marijuana smoke causes THC to enter the bloodstream. From there, it can increase heart rates and lead to dangerous effects like heart rhythm disorders, heart attacks, heart disease, or strokes, according to American Addiction Centers and the American College of Cardiology.

Mental Illness

There is also evidence that with long-term marijuana use, risk of chronic psychosis disorders increases. This includes schizophrenia, general hallucinations, delusions, paranoia, anxiety, depression, suicidal thoughts, and more.

Many teens believe that smoking weed is okay because it calms them down and may minimize the short-term effects of the conditions listed above. However, it is important to consider the long-term effects of marijuana and the fact that continued cannabis use may lead not just to clear physical symptoms, but to mental symptoms, too, especially for those predisposed to such mental conditions.


Any links between marijuana use and cancer are still being explored. There does not seem to be any definitive research that connects cannabis and cancer in a causal way. However, some suspect that marijuana may affect a person's risk for testicular cancer or lung cancer, but there is still much research to be done in at the intersection of marijuana and cancer. Currently, scientists say that the potential is there but cannot be yet confirmed.

Pregnant or Nursing Mothers a photo of a boy toddler doing a puzzle to go along with the paragraph detailing the long-term effects of marijuana if a pregnant person uses

American Addiction Centers stresses the seriousness of the risk level for any pregnant or nursing mothers who consume marijuana. Once again, extensive research in this area is lacking. However, there is evidence of long-term harm to the child's memory, and while no specific symptoms have consistently appeared besides this memory threat, researchers warn against marijuana use in all cases surrounding pregnancy, including during, and after pregnancy, especially involving breastfeeding, as toxins can be carried through the breast milk from mother to infant.

A Gateway

Marijuana is so often called a "gateway drug." It almost sounds cliché, but it is, in fact, true. The National Institute on Drug Abuse confirms that people are more likely to use marijuana (and alcohol and tobacco) before trying other drugs. The same source recognizes that the majority of marijuana users do not go on to use more dangerous drugs, but the correlation still exists.

There is also evidence that early and frequent marijuana use may affect the way that the brain processes other drugs, causing "enhanced responses" to other addictive substances.

Overall, putting any substance repeatedly into your body, especially at a high or frequent dosage, is going to affect you. Maybe the results are different case-by-case, but it is important to keep the possible long-term risk factors in mind while enjoying a short-term high. Do keep in mind, as well, that because marijuana is still a Schedule I strictly-regulated drug in the United States, research is not nearly as extensive as it could be due to certain restrictions. However, the conclusions thus far have all been in agreement, recognizing the risks of long-term marijuana use.