What is marijuana?

Marijuana, also known as cannabis, is a mind-altering drug from the Cannabis plant. It’s used recreationally for its mind-altering effects.

There are roughly 100 unique cannabinoids in cannabis. Tetrahydrocannabinol (THC) and cannabidiol (CBD) are the most widely known cannabinoids. THC is the main chemical that causes the mind-altering effects of marijuana, while CBD is said to have both anti-inflammatory and analgesic effects. Scientifically, there are many unknowns regarding marijuana. There’s still a lot to learn about CBD and THC, and minimal information on the other cannabinoids.

How do people use marijuana?

People may use marijuana in several different ways:

  • Joints: Hand-rolled cigarettes.
  • Blunts: Emptied cigars refilled with marijuana.
  • Bongs: Pipes or water pipes.
  • Edibles: Mixed in foods.

Is marijuana safe to use?

Marijuana use continues to climb, and you may feel it's a safe drug. But problems caused by marijuana use include:

  • Asthma.
  • Lung damage.
  • Brain damage and memory loss.
  • Changes in sex drive.
  • Slowed reaction time.
  • Death from impaired driving.
  • Decreased immunity to illnesses.
  • Lack of motivation.
  • Depression.
  • Anxiety.
  • Panic attacks.
  • False beliefs.
  • Unfounded fear or distrust.
  • Psychosis.
  • Withdrawals.
  • Addiction.

What are some effects of marijuana?

Smoking marijuana puts THC directly into the lungs, where it quickly enters the bloodstream. THC travels in blood to the brain and other organs. Common effects of THC in the brain include:

  • Altered senses (like smell, taste, touch).
  • Altered sense of time.
  • Difficulty thinking or solving problems.
  • Memory problems.
  • Mood changes.

In larger doses, marijuana can cause more serious mental effects of:

  • Confusion.
  • Hallucinations.
  • Paranoia.

What are some long-term health problems associated with marijuana?

Many people believe that marijuana doesn’t have harmful effects like alcohol or other drugs. But marijuana use does affect brain development. In studies of people ages 13 to 38 years, heavy marijuana smoking in their teenage years caused them to lose an average of eight IQ points. Other studies show noticeable declines in general knowledge and verbal ability with marijuana use.

Marijuana concentrations are much stronger today than in previous decades. During the 1990s, marijuana typically contained less than 4% THC. By 2018, the amount of THC was almost four times higher, over 15%. Concentrated marijuana preparation can be as strong as 80% THC. Vaping marijuana, or smoking it with an e-cigarette, is one way people inhale concentrated amounts of THC. E-cigarette or vaping product use-associated lung injury (EVALI) is a new and life-threatening condition diagnosed in people after vaping marijuana.

Marijuana contains more than 2,000 chemicals — including cancer-causing chemicals like cigarettes. These damaging chemicals stay in your body for up to a month. They make it difficult for the body to fight illness and can harm the heart, lungs, brain and sex organs.

How can you tell if someone is using marijuana?

Symptoms of marijuana inhalation are easy to notice. A person using marijuana may:

  • Be forgetful.
  • Feel very hungry.
  • Have dizzy spells and be clumsy.
  • Have red or bloodshot eyes.
  • Laugh for no reason.

Some clinical tests can detect marijuana. A urine test can find traces of THC in someone who consumes marijuana for up to two or three days. In frequent users, urine tests can be found positive for up to 27 days.

What is marijuana addiction?
Like other drugs, marijuana can cause addiction, which is formally called “cannabis use disorder.” When a person becomes addicted, they need more marijuana to get the desired effects. Once addicted, a person might:

  • Have a strong desire or urge to use.
  • Behave less responsibly (like miss work or school).
  • Focus on getting marijuana at the expense of other activities.
  • Spend more time and money on the habit.
  • Withdraw from family and friends.
  • Unable to cut down or control use.
  • Can experience withdrawal symptoms upon ceasing use.

In 2015, an estimated four million Americans have cannabis use disorder. Unfortunately, fewer than 200,000 sought treatment.

How is cannabis use disorder treated?

Treatment starts with counseling. During the counseling session, the person deals with any emotional issues that led to them use marijuana. They also learn strategies to help them quit. No medications are FDA approved to treat cannabis use disorder.

How can I help someone misusing marijuana?

When a friend or family member experiences drug addiction, it’s not always easy to help. People who use marijuana rarely consider the habit problematic or uncontrolled. Remember these pointers when talking to them about their drug use:

  • Shaming someone to quit drug use rarely works. The feeling of shame often causes drug use.
  • Never confront a person who is high or drunk. Wait until they are sober, and then tell them how you feel when they are using.
  • Don’t lend the person money for drugs. That just continues the cycle.
  • Encourage your loved one to get help.
  • Get support for yourself. A counselor can help you find effective strategies to help your friend.

Where can I seek help for marijuana use?

Help is always available to anyone dealing with substance abuse. If you or someone you know are struggling with marijuana addiction, you can find support. Call the Substance Abuse and Mental Health Services Administration helpline at 1-800-662-HELP (4357).

A note from Cleveland Clinic

Marijuana use is not always harmless and can lead to addiction. Dealing with any addiction is hard, but you can overcome it. Talk to your healthcare provider to learn about health effects of marijuana and start your road to recovery.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 12/28/2020.

Learn more about our editorial process.


  • Centers for Disease Control and Prevention. Marijuana and Public Health. (https://www.cdc.gov/marijuana/index.htm) Accessed 1/4/2021.
  • National Center for Complementary and Integrative Health. Cannabis (Marijuana) and Cannabinoids: What You Need to Know. (https://www.nccih.nih.gov/health/cannabis-marijuana-and-cannabinoids-what-you-need-to-know) Accessed 1/4/2021.
  • National Institute on Drug Abuse. Marijuana. (https://www.drugabuse.gov/drug-topics/marijuana) Accessed 1/4/2021.
  • National Institute of Drug Abuse. Marijuana Concentrates DrugFacts. (https://www.drugabuse.gov/publications/drugfacts/marijuana-concentrates) Accessed 1/4/2021.
  • National Institute of Drug Abuse. Marijuana (Weed, Pot) Facts. (https://easyread.drugabuse.gov/content/marijuana-weed-pot-facts) Accessed 1/4/2021.
  • Partnership to End Addiction. Vaping and Marijuana: What You Need to Know. (https://drugfree.org/article/vaping-and-marijuana-what-you-need-to-know/) Accessed 1/4/2021.

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