Marijuana long-term effects?

Dear Alice,

Does marijuana have any real, lasting effects?


Dear Cannabis,

The side effects of marijuana (a.k.a., pot, weed, herb, and many other names!) use are highly debated — by both politicians and health care professionals. Marijuana use for recreational and medicinal purposes has existed for quite some time (Mayo Clinic estimates medicinal use began as early as the mid-19th century). Interestingly, the politics of marijuana use and studies related to the effects on the body and its medicinal value continue to shift and reveal a myriad of potential benefits and risks. Your question, while simple, highlights the significance of our evolving understanding of this drug.

Marijuana can enter the body in a number of ways. It can be smoked, ingested through food, inhaled through vapor, or steeped as a tea. The way marijuana enters the body can impact the type of effects for a person’s experience. Smoking pot causes the substance to enter the bloodstream directly, while oral consumption is first processed in the liver. Some studies indicate that when THC is taken by mouth, a substance is then produced in the liver that can alter mood or consciousness. There are also derivatives of the plant, such as delta-9-tetrahydrocannabinol (THC) and other cannabinoids (chemical components of the cannabis plant), which can be extracted and taken on their own.

Among the research that's currently available, there are mixed conclusions about the side effects associated with the use of marijuana and its various cannabinoids, including:

  • Addiction: Some research studies document that people who attempted to quit marijuana after long-term use experienced symptoms of withdrawal, including anxiety, irritability, sleeplessness, decreased appetite, and marijuana cravings. Various researchers argue that experiencing these symptoms after attempting to abstain from use of marijuana is proof that the substance can be habit forming. Other researchers counter this conclusion, stating there's not enough evidence to support a blanket claim that marijuana is addictive.
  • Appetite and reduced pain: For patients with HIV or cancer, multiple reports show cannabinoid use can improve appetite, reduce nausea, and reduce pain. Additionally, studies have shown that marijuana use improved reported quality of life in patients with multiple sclerosis and fibromyalgia. Research relating to medical, or prescribed, marijuana use explores further potential benefits in additional disease conditions.
  • Fetal development: One of the areas of agreement, amongst both supporters and opponents of marijuana use, is the negative impact on a developing fetus or a breastfeeding child. If used by a breastfeeding parent, marijuana and cannabinoids can be found in breast milk and directly passed to a breastfeeding infant.
  • Lung health: So far, there's no consensus about the connection between lung cancer and smoking pot. However, there is some speculation about how the frequency of use (i.e., heavy versus occasional use) may impact lung cancer risk. The National Institute for Health (NIH) cautions that smoking (no matter what the substance) is still an irritant to the lungs. Marijuana smokers may experience similar respiratory symptoms to those of tobacco smokers, such as frequent cough, increased phlegm, elevated risk of lung infections, and more frequent acute chest illness.
  • Mental and emotional health: Some researchers argue that pot can help reduce anxiety, while others claim its use can exacerbate mental illness and even induce short-term psychosis, including hallucinations and paranoia. Some studies describe a wide range of potential mental and emotional side effects of marijuana (enjoyable for some and distressing for others), including confusion, anxiety, inability to concentrate, sleepiness, and even feelings of exhilaration. 
  • Other physical side effects: Marijuana can cause various other physical side effects including decreased blood pressure, increased heart rate or heart palpitations, lightheadedness, and slower than normal reaction time. Long-term, regular use has been shown to induce cycles of nausea, vomiting, and dehydration classified as Long-Cannabinoid Hyperemesis Syndrome. Additionally, some users report instances of acute psychomotor impairment, making it risky to operate a vehicle or perform other essential functions while high.

In addition to these possible side effects, a hot topic of debate in the field is the correlation between age-related marijuana use and brain functions such as memory and learning. Several studies have observed that adolescents who frequently use marijuana display signs of neuropsychological decline, impaired intellectual functioning, and lower IQ overall. In comparison, study participants who began to use marijuana as adults didn't experience the same mental decline. This is thought to be because the adolescent brain is still in development. Changes to the endocannabinoid system (responsible for regulating homeostasis) by marijuana during adolescence may affect neural development. Quitting marijuana use as an adult didn't seem to fully restore those losses of brain functionality. While the present research is limited and there's still so much more to learn, appreciating the association between age-related marijuana use and cognitive impairment helps to understand the reasoning behind government regulations on the legal age for marijuana consumption.

The use of marijuana is banned by federal law, but also legalized for medicinal purposes in several states. This juxtaposition may be partially explained by the divided conclusions that exist surrounding the impact of marijuana on a person’s health. The diversity among marijuana plants and the cannabinoids found in different samples can pose a challenge to more generalizable research results. With time and additional study, hopefully more clear conclusions will surface about the benefits and risks of marijuana use.

Hope this helps!

Last updated Dec 03, 2021
Originally published Oct 01, 1993