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.
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). Some people mix it into food or brew it as a tea.
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. When these nerve cells are in the parts of the brain that govern sensory perception and pleasure, it causes the marijuana "high."
THC also connects with receptors on nerve cells in other parts of the brain. When those parts of the brain affect thinking, memory, coordination, and concentration, it can cause unwanted side effects, including:
difficulty thinking and problem solving
problems with memory and learning
loss of coordination
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:
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 in women. Women who use marijuana when they are pregnant may 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 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.
Some states are changing their laws to make it legal to have small amounts of marijuana in certain situations (like when it's prescribed for medical use). But many states still have laws against using, growing, or selling marijuana — and people caught with it could face charges, including jail time.
Here are a few ways marijuana use could affect you:
Criminal charges. Marijuana laws can be confusing. For example, a state might allow people to have a small amount of marijuana with a doctor's prescription — but the same state's laws make it illegal to buy, sell, or grow it.
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. It can take up to 12 days for marijuana to leave the body. 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.
The U.S. Food and Drug Administration (FDA) has approved pills containing as a way to help relieve pain, nausea, muscle stiffness, or problems with movement — particularly for people with cancer or AIDS.
There's still a lot of discussion about the medical use of marijuana, though. So the THC pill is only available in some states and requires 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 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 worst 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.
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.