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Reviewed by: Steven Dowshen, MD

What Is Marijuana?

Marijuana is a shredded, green-brown mix of dried flowers, stems, and leaves from the plant Cannabis sativa. A stronger form of marijuana, called hashish (hash), looks like brown or black cakes or balls. The amount of THC (the active ingredient) in marijuana and marijuana products has increased greatly over the years.

Marijuana is usually rolled and smoked like a cigarette (joints or doobies), or put in hollowed-out cigars (blunts), pipes (bowls), or water pipes (bongs). Recently, it has become increasingly popular for people to inhale marijuana or stronger marijuana extracts using a vaporizer (called "vaping" or "dabbing"). Some people mix it into food or brew it as a tea.

There is also "synthetic marijuana" — manmade drugs that are chemically similar to THC — that can be dangerously strong. Names for these drugs include "K2," "Spice," and "Herbal Incense." They can be so potent that overdose deaths have happened.

Short-Term Effects

The main active chemical in marijuana is THC (delta-9-tetrahydrocannabinol). When someone smokes marijuana, THC goes from the lungs into the bloodstream. From there, it ends up in the brain and other organs.

THC connects with a receptor on nerve cells in the brain. The marijuana "high" results from THC's effects on the nerve cells that control sensory perception and pleasure.

THC also connects with receptors on nerve cells in other parts of the brain that affect thinking, memory, coordination, and concentration. This can cause unwanted side effects, including:

  • trouble thinking and problem solving
  • problems with memory and learning
  • loss of coordination
  • distorted perception

These side effects are temporary, but they can make it dangerous to do things like drive while under the influence of marijuana.

People also might notice other short-term side effects of using marijuana, such as:

  • an increased appetite
  • feeling lightheaded or drowsy
  • a decrease in inhibitions

Long-Term Effects

Research has found that people who use marijuana over a long period of time can have more lasting side effects. For example:

Changes in the brain. Marijuana can affect the parts of the brain that play a role in our ability to remember, multitask, and pay attention.

Fertility issues. Animal studies suggest that using a lot of marijuana might be linked to decreased sperm count in men and delayed ovulation in women. Pregnant women who use marijuana might be more likely to have babies with developmental and behavioral problems.

Respiratory problems. People who smoke marijuana a lot can develop problems with the respiratory system — like more mucus, a chronic cough, and bronchitis.

Immune system problems. Using marijuana a lot might make it harder for the body to fight off infections.

Emotional problems. People who use a lot of marijuana are more likely to say they notice signs of depression or anxiety. If someone has a condition like schizophrenia or bipolar disorder, marijuana can sometimes make symptoms worse.

Other Problems

Here are a few ways marijuana use could affect you:

Criminal charges. Marijuana laws can be confusing. Some states are changing their laws to make it legal to have small amounts of marijuana in some situations (like when it's prescribed for medical use). Some have even made recreational use of marijuana by adults (over 21) legal. But there are conflicting federal laws against using, growing, or selling marijuana — and people caught with it could face charges, including jail time.

Career problems. People charged under marijuana laws may end up with criminal records that hurt their plans for college or finding a job.

Drug testing. These days, employers often test for drug use as part of the hiring process. Marijuana can show up on a drug test for several weeks after it was last used. So people who use marijuana may find they don't get a job they want. Some companies do routine drug tests on employees, so people who use marijuana can lose their jobs.

Medical Use of Marijuana

The U.S. Food and Drug Administration (FDA) has approved pills containing THC or other cannabinoids (chemicals similar to THC) as a way to help relieve pain, nausea, muscle stiffness, or problems with movement. There's still a lot of discussion about the medical use of marijuana, though. THC and other cannabinoid pills are only available in some states and require a doctor's prescription.

At the moment, there's not enough research to say for sure if smoking marijuana is any more helpful than taking THC or other cannabinoids as a pill. Scientists are still studying this.

What If I Want to Quit?

People who use marijuana for a while can have withdrawal symptoms when they try to give it up. They may feel irritable, anxious, or depressed; have trouble sleeping; or not feel like eating.

Marijuana withdrawal can be a bit like caffeine withdrawal: It's usually worse a day or two after someone stops using marijuana. After that, withdrawal symptoms gradually decrease. They're usually gone a week or two after the person no longer uses the drug.

Marijuana can be addictive. About 1 in 10 people who use the drug regularly can develop a "marijuana use disorder." These people can't stop using marijuana even though it causing problems in their lives. This is much more likely to happen in people who start using marijuana before age 18.

If you or someone you know wants to stop using marijuana but has trouble quitting, it can help to talk to a counselor. Studies suggest that a combination of individual counseling and group therapy sessions is the best approach for stopping marijuana use.

Reviewed by: Steven Dowshen, MD
Date reviewed: May 2018