Whether you smoke marijuana, drink alcohol, or snort cocaine, there are risks involved with using drugs that can range from addiction to death. Knowing the risks can help you make better decisions that positively affect your health.

Emotional and physical responses to recreational drugs vary, depending on the person and the substance being abused, says Gregory B. Collins, MD, section head of the Alcohol and Drug Recovery Center at the Cleveland Clinic Foundation.

Understanding the effects of these drugs on your body and the serious threat of addiction they pose is the first step in protecting yourself.

Marijuana. This mild hallucinogen, derived from the Cannabis sativa plant, is the most commonly abused illegal drug in the United States, according to the National Institute on Drug Abuse. When used, usually through smoking, marijuana acts as a central nervous system stimulant. “It speeds up heart rate and raises blood pressure,” Dr. Collins says. “It can stimulate the nervous system enough that some people become paranoid while taking it.” At the same time, marijuana can dull memory, making it harder to concentrate or remember things.

Death from smoking too much marijuana is rare, but as with smoking cigarettes, habitual marijuana use can lead to heart disease and other cardiovascular problems. “There are a lot of substances in a marijuana joint,” Collins says. “You’re introducing a dirty substance into your lungs.” And just like tobacco smokers, marijuana smokers are at risk for respiratory problems such as chronic cough and frequent lung infections. Marijuana smoke also contains many carcinogens, though a definitive link between it and cancer remains unclear at this time.

In a recent U.S. survey by the Substance Abuse and Mental Health Services Administration, more than 4.5 million people ages 12 and over indicated that they were dependent on or abused marijuana.

Cocaine. A powerful, addictive stimulant, cocaine gives users a euphoric feeling when ingested, which, depending on the person, may or may not actually feel good. “Some people experience that rush as very pleasurable, but others don’t like it,” Collins says. The euphoric feeling is short-lived, lasting anywhere from 30 to 45 minutes.

Cocaine is usually snorted as a powder, but it can also be modified into rock form — so-called crack — and smoked. Cocaine tightens blood vessels and speeds up the heart. These cardiovascular effects are the main reason for most cocaine-related deaths. “Even in small doses, it can kill you,” Collins says. “Sudden death is not uncommon.”

Approximately 16 percent of Americans 12 and older have used cocaine at least once in their lifetime, according to the Office of National Drug Control Policy. In the Substance Abuse and Mental Health Services Administration survey, about 1 million people age 12 and over said they were dependent on cocaine, down from 1.1 million the year before.

Opiates. These drugs, which include both street drugs like heroin and pharmaceutical painkillers like morphine and codeine, act on the body’s central nervous system by stimulating the brain’s “reward center,” which controls pleasurable feelings. Opiates mimic the effects of healthy feel-good activities, like having sex or eating. However, in high doses, opiates can cause some of the brain’s critical functions, like breathing, to slow down or stop working. In an overdose “the brain shuts off the ‘thermostat’ that drives respiration,” Collins says. “The person goes into a coma and dies.”

Since heroin is commonly injected, users are also at risk for HIV and hepatitis, which can be transmitted through shared needles.

In a 2010 U.S. survey, nearly 359,000 Americans ages 12 and over considered themselves dependent on heroin, up significantly from 214,000 in 2002.

Methamphetamine. Usually a white powder that is smoked, snorted, or injected, this powerful stimulant is highly addictive. Like cocaine, methamphetamine (often known simply as "meth") can speed up the heart, as well as cause hyperthermia, an extremely high body temperature. When used over a long period of time, methamphetamine can cause anxiety, insomnia, and even psychotic symptoms, like hallucinations. Severe dental problems can also occur; the drug is acidic and can wear down teeth over time. Users often grind their teeth as well, further damaging them.

As with heroin users, people who inject methamphetamine are at risk for HIV and hepatitis.

According to the national survey on drug use and health, about 13 million Americans ages 12 or older have used methamphetamine at least once in their lifetime. About 277,000 people over age 12 consider themselves dependent on stimulant drugs, a slight increase over the year before.

Alcohol. Moderate consumption of alcohol is safe for most people, but heavier use can lead to problems. Over the long term, having more than one alcoholic drink per day for women or anyone over 65 or two drinks per day for men under 65 can increase a person's risk of developing medical conditions like pancreatitis and liver and heart disease.

Alcohol also has short-term health effects. Since alcohol is a depressant, it can slow motor skills and impair the user's ability to make clear judgments. Additionally, a woman who uses alcohol while pregnant puts her unborn child at risk for fetal alcohol syndrome, a condition that can cause mental retardation, impaired vision, and other lifelong problems.

About 14 million people in the United States either abuse alcohol or are alcoholics, according to the National Institute on Drug Abuse.

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