Drug Facts: Marijuana

First published 2003. To view the latest Heads Up content, click here.
DIA receptors

Say good-bye to the myth that marijuana is a harmless drug. Check out these facts. 

THC Invasion
The relaxed feeling marijuana users experience is caused by THC (tetrahydrocannabinol), the active ingredient (the chemical most responsible for an observed effect) in marijuana. But the chemical also causes negative side effects.

Here’s what happens: When a user smokes marijuana, the THC travels quickly through the bloodstream to the brain. That’s when the problems start. In everyone’s brain, there are special receptors, called cannabinoid receptors. They’re located in several important brain regions, including the area that helps you remember things. THC attaches to the cannabinoid receptors and interferes with the brain’s normal functioning.

The Lungs, Too
It’s not just the brain. Smoking marijuana messes with the lungs, too. Here’s some of what science tells us:


  • Marijuana smokers can develop phlegm and a daily cough.
  • Marijuana smoke contains 50 to 70 percent more cancer-causing chemicals than tobacco smoke.
  • People who smoke marijuana are at greater risk for lung infections, such as pneumonia.
  • Chronic marijuana smokers are vulnerable to bronchitis, emphysema, and bronchial asthma.
  • Scientists have found signs of lung tissue that has been injured or destroyed due to marijuana use.

The Addiction Question
Marijuana can be addictive. For some people, this is a controversial idea. They argue marijuana is not addictive. According to NIDA, addiction is characterized by “compulsive, at times uncontrollable, drug craving, seeking, and use that persists even in the face of extremely negative consequences.”

Dr. Nora Volkow, the director of NIDA, says that marijuana is indeed addictive. “I find it ironic that people say, ‘Oh, it’s not addictive,’ and yet it’s the most commonly used of our illicit [illegal] drugs,” she says.

It is certainly true that not everyone who smokes marijuana becomes addicted, yet many people experience cravings for the drug and have withdrawal symptoms when they get off it. And that’s addiction.


Browse Other Content