What happens when someone smokes cannabis?

The way cannabis affects each person depends on many factors, including the user’s previous experience with the drug, the strength of the strain, the user’s expectations, how the drug is consumed, and whether the person has been drinking or using other drugs. Effects of cannabis can include:

  • Feelings of relaxation or feeling “high”
  • Increase in appetite and thirst
  • Feelings of anxiety and paranoia
  • Distorted perceptions
  • Trouble with thinking and problem solving
  • Loss of motor coordination
  • Problems with memory and learning
  • Disrupted sleep
  • Physical effects, such as increased heart rate and breathing problems

These can impact a person’s learning, academic performance, relationships, and athletic performance.

What is the active ingredient in cannabis?

All forms of cannabis are mind-altering. In other words, they change how the brain works. The main active chemincal in cannabis is THC (delta-9-tetrahydrocannabinol). Cannabis' affects on users depends on its strength or potency, which is related to the amount of THC it contains.

How long does cannabis stay in the user's body?

The THC in cannabis is rapidly absorbed by fatty tissues in various organs. Generally, traces of THC can be detected by standard urine tests several days after cannabis has been used. In chronic heavy users, traces can sometimes be detected for weeks after someone stops using.

What are the long-term effects of cannabis use?

Findings show that regular use of cannabis or THC may play a role in some kinds of cancer. Studies show that someone who smokes five joints per day may be taking in as many cancer-causing chemicals as someone who smokes a full pack of cigarettes every day.

Smoking cannabis can also cause problems in the respiratory and immune systems. People who smoke cannabis often develop the same kinds of breathing problems that cigarette smokers have, including coughing and wheezing. They also tend to have more chest colds and are at greater risk of getting lung infections. 

What does cannabis do to the brain?

Some studies show that when people smoke large amounts of cannabis for years, the drug takes its toll on mental functions. Heavy or daily use of cannabis affects the parts of the brain that control memory, attention, and learning. A working short-term memory is needed to learn and perform tasks that call for more than one or two steps.

How does cannabis affect driving?

Cannabis impairs the skills required to drive safely: alertness, concentration, coordination, and reaction time. Cannabis use can make it difficult to judge distances and react to signals and sounds on the road. Data have also shown that while smoking cannabis, people show the same lack of coordination on standard "drunk driver" tests as do people who have had too much to drink.

Can people become addicted to cannabis?

Yes, long-term cannabis use can lead to addiction in some people, meaning that they cannot control their urges to seek out and use cannabis, even though it negatively affects their family relationships, school performance, and recreational activities. Also, some frequent, heavy cannabis users develop “tolerance” to its effects. This means they need larger and larger amounts to get the same desired effects as they used to get from smaller amounts.

What if someone wants to stop using cannabis?

In 2002, over 280,000 people entering drug treatment programs reported cannabis as their primary drug of abuse. However, up until a few years ago, it was hard to find treatment programs specifically for cannabis users. Now researchers are testing different ways to help cannabis users abstain from drug use. There are currently no medications for treating cannabis addiction. Treatment programs focus on counseling and group support systems.

For more information, see the National Institute on Drug Abuse website.