Topic Overview

What is marijuana?

Marijuana, also called cannabis, is a drug that is made up of the leaves, flowers, and buds of the hemp plant Cannabis sativa. It is often smoked in pipes or hand-rolled cigarettes. But it can also be vaporized, applied to the skin, cooked in food, or brewed into tea.

In the United States, it's against federal law to possess, sell, give away, or grow marijuana for any purpose. But many states have passed laws that allow people with certain health problems to buy or grow it for their own use. And some states allow people to use it for non-medical reasons. These laws vary from state to state. You can call your state department of health or health services to learn more about the laws in your state.

What are the short-term effects of marijuana?

People often use marijuana for the way it makes them feel. Using it may make them:

  • Feel relaxed or very happy ("high").
  • Have less chronic pain or nerve (neuropathic) pain.
  • Feel hungry so they eat more.

But it may also cause unwanted side effects, such as:

  • Impaired short-term memory.
  • Poor judgment and coordination. It can increase the risk of being in a car crash.
  • Anxiety or paranoid thoughts.
  • Faster heart rate.
  • Red eyes and dry mouth.
  • Nausea and vomiting.

The immediate effects of marijuana depend on the potency of its main active chemical, THC. THC affects areas of the brain that are involved in important functions such as memory, concentration, and coordination.

How quickly the effects start depends on several things, including how it was taken. When marijuana is smoked, the effects can usually be felt within seconds after inhaling. The effects last about 2 to 3 hours.

Marijuana is absorbed by fatty tissues in various organs of the body. THC usually can be detected in urine several days after marijuana has been smoked. If marijuana use is heavy, THC may be found in urine for weeks after use has stopped.

What are the long-term effects of marijuana use?

Long-term regular use of marijuana may cause problems such as:

  • Trouble with learning and memory. This is most likely if regular heavy use begins in the teen years.
  • Reduced lung function. This can lead to coughing or wheezing.
  • An increased risk of lung cancer. But the risk seems to be much less than the risk from smoking tobacco.

Can marijuana use lead to cannabis use disorder?

Some people who regularly use marijuana may develop cannabis use disorder. This means that they keep using marijuana even though it's having harmful effects on their lives.

The risk of cannabis use disorder is higher in people who:

  • Start using marijuana when they're young.
  • Use it every day.
  • Have mental health problems.

People who use marijuana often and then quit may have withdrawal symptoms. These include anxiety, trouble sleeping, and intense cravings for the drug.

What is synthetic marijuana?

Synthetic marijuana is made of dried plant material that is treated with chemicals that produce effects like marijuana's effects. It is sold in the form of incense under many names, such as K2 or Spice. The labels often claim that these products are "safe" or "natural." But in fact, the active chemicals are created in a lab. And they have not been tested for safety.

But young people often try these products because they are easy to buy and they may not be detected by drug tests.

People think that using these drugs will make them feel the same as when they use marijuana. But these drugs are stronger than marijuana. And the effects are hard to predict. That's because the type and strength of the chemicals used are often unknown. Some people have reported severe symptoms, such as:

  • Fast heart rate and high blood pressure.
  • Vomiting.
  • Feeling agitated or confused.
  • Feeling like others want to harm them (paranoia), or seeing or hearing things that aren't there (hallucinations).


Other Works Consulted

  • American Lung Association (2012). Health hazards of smoking marijuana. Available online:
  • National Cancer Institute (2013). Cannabis and Cannabinoids PDQ – Health Professional Version. Available online:
  • National Institute on Drug Abuse (2012). DrugFacts: Marijuana. Available online:
  • National Institute on Drug Abuse (2012). DrugFacts: Spice (Synthetic Marijuana). Accessed September 30, 2013.


Current as of: June 29, 2020

Author: Healthwise Staff
Medical Review: Patrice Burgess MD - Family Medicine
Adam Husney MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Kathleen Romito MD - Family Medicine
Michael F. Bierer MD - Internal Medicine, Addiction Medicine