In the United States, the most commonly used illicit drug is marijuana. Some users and legalization activists feel there are no negative effects to this drug, while some scientific research indicates the drug can cause a variety of different health problems. What are the effects of smoking marijuana?

Marijuana is considered a mild hallucinogen, with some of alcohol’s depressant and dis-inhibiting effects. These reactions, though, are sometimes influenced by expectations and past experience. A good number of first-time users don’t feel anything at all. Generally the effects of smoking are felt within minutes and peak in ten to thirty minutes, and wear off within two or three hours. These effects include dry mouth and throat, increased heart rate, impaired coordination, delayed reaction time, and short-term memory. Moderate doses induce a feeling of well-being and relaxation and distorted perceptions. Stronger doses may lead to intense and disturbing experiences with hallucinations and paranoia.

In the brain, marijuana’s active ingredient, known as delta-9 tetrahydrocannabinol, or more commonly as THC, has an effect on cannabinoid receptors in nerve cells, influencing them. Largely, cannabinoid receptors are in the areas of the brain that control pleasure, sensory and time perception, memory, thought, and coordinated movement. Therefore, when marijuana is used in high doses (usually when eaten, as opposed to being smoked), users can experience hallucinations, impaired memory, disorientation and delusions.

When smoking marijuana, after a few minutes, the heart beats more rapidly and blood pressure drops. The drug can cause the heart to increase by as much as 20 to 50 beats a minute, and, if other drugs are used in combination with marijuana, it may increase even more. Researchers have found that due to higher heart rate and lower blood pressure, a user’s risk for a heart attack is four times higher within the first hour after smoking the drug.

Even infrequent smoking marijuana may cause effects to the lungs, including a burning and stinging of the mouth and throat, as well as heavy coughing. Regular users of marijuana who smoke it may experience similar problems with their respiratory system as tobacco smokers do, such as daily coughing and phlegm production; a possibility of lung infections; obstructed airways; and frequent illnesses of the chest. It’s true, though, that marijuana smokers consume less cannabis than cigarette smokers do tobacco; however, marijuana does contain carcinogenic hydrocarbons, even more than tobacco smoke. Marijuana smokers hold the smoke in the lungs longer than tobacco smokers, too, which expose the lungs to the carcinogenic properties longer.

While one study suggested that marijuana smokers were three times as likely to develop cancer of the head or neck than non-smokers, further studies couldn’t confirm this finding. There is a problem with studies that investigate cancer dangers with marijuana smokers: marijuana smokers are also often cigarette smokers; therefore, the information is mixed — are cancer dangers caused by marijuana, tobacco, or both?

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