Weed, also known as marijuana, is a drug derived from the leaves, flowers, stems, and seeds of either the Cannabis sativa or Cannabis indica plant. There is a chemical in the plants called tetrahydrocannabinol (THC) that has mind-altering properties.

According to the National Institute on Drug Abuse (NIDA), marijuana is the most commonly used illicit drug in the United States. Although nine states, plus Washington, D.C., have legalized marijuana for general use and 29 others have legalized medical marijuana, many more states still consider it to be an illicit substance.

Marijuana, and THC in particular, has been shown to reduce chemotherapy-induced vomiting and nausea for people going through cancer treatment. It can also help to reduce nerve damage pain (neuropathy) in people with HIV or other conditions.

According to NIDA, approximately 30 percent of marijuana users may have some sort of marijuana use disorder. It’s estimated that between 10 and 30 percent of individuals who smoke weed will develop dependency, with only 9 percent actually developing addiction. However, exact statistics are unknown.

A substance use disorder starts in the form of dependence, or experiencing withdrawal symptoms when the drug is stopped or not ingested for a period of time. Dependence occurs when your brain gets used to weed being in your system and, as a result, reduces its production of endocannabinoid receptors. This can result in irritability, mood swings, sleep problems, cravings, restlessness, and lack of appetite for several weeks after stopping. This is different than addiction.

Addiction occurs when a person experiences changes in their brain or behavior as a result of the drug. It’s possible to be dependent without being addicted, so there aren’t reliable statistics on marijuana addiction, says NIDA.

In 2015, approximately 4 million people met the diagnostic criteria for a marijuana use disorder. According to the National Institute on Alcohol Abuse and Alcoholism, that same year, approximately 15.1 million adults in the United States over the age of 18 met the criteria for alcohol use disorder. In 2016, the Centers for Disease Control and Prevention (CDC) found that approximately 37.8 million adults in the United States currently smoked cigarettes.

Different strains of marijuana can have different amounts of THC, and depending on who is distributing the weed, there’s always a risk of other chemicals or drugs lacing it. Marijuana provided by medicinal dispensaries is generally considered safe. Side effects can occur at any time, although some side effects are dose dependent, as mentioned below.

Some side effects of weed can include:

  • headache
  • dry mouth
  • fatigue
  • dry eyes
  • increased appetite (commonly called “the munchies”)
  • coughing
  • dissociation or altered state
  • altered sense of time
  • dizziness or lightheadedness
  • high blood pressure
  • impaired memory

In very high doses, weed can also cause hallucinations, delusions, or psychosis. This is rare, though, and not the norm. Some experts believe that people who experience psychosis from marijuana may already be at risk for psychosis.

In some people with bipolar disorder, weed might worsen manic states. Frequent use of marijuana might increase depression symptoms and the risk of depression. If you have a mental health condition, this is something to consider and perhaps speak with your doctor or therapist about.

If you take any medications, either prescription or over-the-counter, it’s worth checking to see if there are any possible interactions. Weed can increase the effects of alcohol, negatively interact with blood clotting medications, and increase the risk of mania in people who take SSRI antidepressants. Talk with your doctor about the medications and supplements you are taking, and whether there are any known adverse interactions with weed.

Marijuana can be beneficial to a variety of individuals, especially those living with certain conditions causing pain, intense vomiting, or severe lack of appetite. Like many medications or supplements, weed might have the potential to become addictive in some individuals.

Addiction involves a number of factors, and the lack of clear statistics on weed makes this a complicated topic. If you’re worried about the potential for addiction, talk with your doctor about your concerns.