Marijuana—also called weed, herb, pot, grass, bud, ganja, Mary Jane, and a vast number of other slang terms—is a greenish-gray mixture of the dried flowers of Cannabis sativa. Some people smoke marijuana in hand-rolled cigarettes called joints; in pipes, water pipes (sometimes called bongs), or in blunts (marijuana rolled in cigar wraps). Marijuana can also be used to brew tea and, particularly when it is sold or consumed for medicinal purposes, is frequently mixed into foods (edibles) such as brownies, cookies, or candies. Vaporizers are also increasingly used to consume marijuana. Stronger forms of marijuana include sinsemilla (from specially tended female plants) and concentrated resins containing high doses of marijuana’s active ingredients, including honeylike hash oil, waxy budder, and hard amberlike shatter. These resins are increasingly popular among those who use them both recreationally and medically.

Marijuana, which can also be called weed, pot, dope, or cannabis, is the dried flowers and leaves of the cannabis plant. It contains mind-altering (e.g., psychoactive) compounds like tetrahydrocannabinol, or THC, as well as other active compounds like cannabidiol, or CBD, that are not mind-altering.

The main psychoactive(mind-altering) chemical in marijuana, responsible for most of the intoxicating effects that people seek, is delta-9-tetrahydrocannabinol (THC). The chemical is found in resin produced by the leaves and buds primarily of the female cannabis plant. The plant also contains more than 500 other chemicals, including more than 100 compounds that are chemically related to THC, called cannabinoids.

How is marijuana used?

There are many ways of using marijuana, and each one affects users differently. Marijuana can be rolled up and smoked like a cigarette (a joint) or a cigar (a blunt). Marijuana can also be smoked in a pipe. Sometimes people mix it in food and eat it or brew it as a tea (edibles). Smoking oils, concentrates, and extracts from the marijuana plant are on the rise. People who use this practice call it “dabbing.”

What determines how marijuana effects a person?

Like any other drug, marijuana’s effects on a person depends on a number of factors, including the person’s previous experience with the drug or other drugs, biology (e.g., genes), gender, how the drug is taken, and how strong it is.

How do marijuana work?

The human body naturally produces some cannabinoids through the endocannabinoid system. They act in a similar way to neurotransmitters, sending messages throughout the nervous system.

These neurotransmitters affect brain areas that play a role in memory, thinking, concentration, movement, coordination, sensory and time perception, and pleasure.

The receptors that respond to these cannabinoids also react to THC and other cannabinoids. In this way, cannabinoids from an outside source can change and disrupt normal brain function.

THC appears to affect areas of the brain that control:

• memory and attention
• balance, posture, and coordination
• reaction time

Due to these effects, a person should not drive a car, operate heavy machinery, or engage in risky physical activities after using cannabis.

THC stimulates specific cannabinoid receptors that increase the release of dopamine. Dopamine is a neurotransmitter that relates to feelings of pleasure.

THC can also affect sensory perception. Colors may seem brighter, music more vivid, and emotions more profound.

Is marijuana medicine?

The marijuana plant has chemicals that may help symptoms for some health problems. More and more states are making it legal to use the plant as medicine for certain conditions. But there isn’t enough research to show that the whole plant works to treat or cure these conditions. Also, the U.S. Food and Drug Administration (FDA)External has not recognized or approved the marijuana plant as medicine.

Because marijuana is often smoked, it can damage your lungs and cardiovascular system (e.g., heart and blood vessels). These and other damaging effects on the brain and body could make marijuana more harmful than helpful as a medicine. Another problem with marijuana as a medicine is that the ingredients aren’t exactly the same from plant to plant. There’s no way to know what kind and how much of a chemical you’re getting.

Two medicines have been made as pills from a chemical that’s like THC, one of the chemicals found in the marijuana plant that makes people feel “high.” These two medicines can treat nausea if you have cancer and make you hungry if you have AIDS and don’t feel like eating. But the chemical used to make these medicines affects the brain also, so it can do things to your body other than just working as medicine.

Another marijuana chemical that scientists are studying, called cannabidiol (CBD), doesn’t make you high because it acts on different parts of the nervous system than THC Scientists think this chemical might help children who have a lot of seizures (when your body starts twitching and jerking uncontrollably) that can’t be controlled with other medicines. Some studies have started to see whether it can help.

What is medical marijuana used for?

Researchers are studying whether medical marijuana can help treat a number of conditions including:

• Alzheimer’s disease
• Appetite loss
• Cancer
• Crohn’s disease
• Diseases effecting the immune system like HIV/AIDS or Multiple Sclerosis (MS)
• Eating disorders such as anorexia
• Epilepsy
• Glaucoma
• Mental health conditions like schizophrenia and posttraumatic stress disorder (PTSD)
• Multiple sclerosis
• Muscle spasms
• Nausea
• Pain
• Seizures
• Wasting syndrome (cachexia)

But it’s not yet proven to help many of these conditions, with a few exceptions, Bonn-Miller says.

The greatest amount of evidence for the therapeutic effects of cannabis relate to its ability to reduce chronic pain, nausea and vomiting due to chemotherapy, and spasticity [tight or stiff muscles] from MS,”

Bonn-Miller says.

How does it help?

Cannabinoids — the active chemicals in medical marijuana — are similar to chemicals the body makes that are involved in appetite, memory, movement, and pain.

Limited research suggests cannabinoids might:

• Reduce anxiety
• Reduce inflammation and relieve pain
• Control nausea and vomiting caused by cancer chemotherapy
• Kill cancer cells and slow tumor growth
• Relax tight muscles in people with MS
• Stimulate appetite and improve weight gain in people with cancer and AIDS

Can medical marijuana help with seizure disorders?

Medical marijuana received a lot of attention a few years ago when parents said that a special form of the drug helped control seizures in their children. The FDA recently approved Epidiolex, which is made from CBD, as a therapy for people with very severe or hard-to-treat seizures. In studies, some people had a dramatic drop in seizures after taking this drug. 

Has the FDA approved medical marijuana?

The cannabidiol Epidiolex was approved in 2018 for treating seizures associated with two rare and severe forms of epilepsy, Lennox-Gastaut syndrome and Dravet syndrome. In addition, the FDA has approved two man-made cannabinoid medicines — dronabinol (Marinol, Syndros) and nabilone (Cesamet) — to treat nausea and vomiting from chemotherapy. The cannabidiol Epidiolex was approved in 2018 for treating seizures associated with two rare and severe forms of epilepsy, Lennox-Gastaut syndrome and Dravet syndrome.

What are the health risks of marijuana?

At the other end of the spectrum is the plethora of studies that have found negative associations between marijuana use and health. They are listed below.

Mental health problems

Daily marijuana use is believed to exacerbate existing symptoms of bipolar disorder among people who have this mental health problem. However, the National Academies of Sciences, Engineering, and Medicine report suggests that among people with no history of the condition, there is only limited evidence of a link between marijuana use and developing bipolar disorder.

Moderate evidence suggests that regular marijuana users are more likely to experience suicidal thoughts, and there is a small increased risk of depression among marijuana users.

Marijuana use is likely to increase risk of psychosis, including schizophrenia. But a curious finding among people with schizophrenia and other psychoses is that a history of marijuana use is linked with improved performance on tests assessing learning and memory.

Testicular cancer

Although there is no evidence to suggest any link between using marijuana and an increased risk for most cancers, the National Academies of Sciences did find some evidence to suggest an increased risk for the slow-growing seminoma subtype of testicular cancer.

Respiratory disease

Regular marijuana smoking is linked to increased risk of chronic cough, but “it is unclear” whether smoking marijuana worsens lung function or increases the risk of chronic obstructive pulmonary disease or asthma.

A 2014 studyTrusted Source that explored the relationship between marijuana use and lung disease suggested that it was plausible that smoking marijuana could contribute to lung cancer, though it has been difficult to conclusively link the two.

The authors of that study — published in the journal Current Opinion in Pulmonary Medicine — conclude:

here is unequivocal evidence that habitual or regular marijuana smoking is not harmless. A caution against regular heavy marijuana usage is prudent.

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Researchers at the National Academies of Sciences, Engineering and Medicine have delivered a motherlode of cannabis research. A committee of scientists reviewed more than 10,000 scientific abstracts published since 1999 to reach nearly 100 conclusions about the health effects of marijuana and cannabis-derived products. For their report, they looked at everything from the risk of developing cancer to the risk of getting into a car accident after using the substance.

Cannabis is America’s favorite illicit drug, with 22 million users ages 12 and older reporting that they used it in the past 30 days. The legal landscape for the drug is shifting across the country, as more and more states legalize it for recreational and medicinal use.

“This growing acceptance, accessibility, and use of cannabis and its derivatives have raised important public health concerns,” said Marie McCormick, chair of the research committee, in a release from the National Academies. McCormick is the Sumner and Esther Feldberg Professor of Maternal and Child Health, department of social and behavioral sciences, Harvard T.H. Chan School of Public Health and a professor of pediatrics at Harvard Medical School.

“The lack of any aggregated knowledge of cannabis-related health effects has led to uncertainty about what, if any, are the harms or benefits from its use,” she said. “We conducted an in-depth and broad review of the most recent research to establish firmly what the science says and to highlight areas that still need further examination. As laws and policies continue to change, research must also.”

The committee’s conclusions include:

• Patients who were treated with cannabis or cannabinoids were more likely to experience a significant reduction in pain symptoms.
• Oral cannabinoids were associated with improved reported symptoms of adults with multiple sclerosis-related muscle spasms.
• Oral cannabinoids showed efficacy in preventing and treating chemotherapy-induced nausea and vomiting.

The researchers recommended further research, while emphasizing the challenges in conducting it, namely marijuana’s classification as a Schedule 1 substance. A diverse network of funders is needed, they said.