It's a parent's nightmare—and for many, it comes true. In the most recent nationally representative survey sponsored by the National Institute on Drug Abuse, half of the nearly 15,000 high school seniors surveyed at 129 schools admitted to using illicit drugs during their lifetime. Forty percent got high in the past year, and one in four in the previous month. The survey offers detailed, and sometimes surprising, revelations about which drugs teens favor. Some may come not from dealers, but from the drugstore or even your own medicine cabinet. Below are the substances of choice for high school seniors. Learning about them can help you spot signs of abuse in your own teen. Marijuana One in 15 seniors smokes pot on a daily or near-daily basis—the highest rate in the past 30 years. Experts say this increase may be because teens no longer see the drug as dangerous. What they fail to realize is that marijuana affects their learning and memory. It also increases their risk for smoking-related health problems, including emphysema, bronchitis, and asthma. There's a new twist to the story: Synthetic marijuana, or spice, a man-made compound designed to mimic pot's effects, has become increasingly popular. It's sold under the names K2, Yucatan Fire, fake weed, Moon Rocks, Skunk, and others. The U.S. Drug Enforcement Agency began regulating it in 2011, making it illegal to buy, sell, or possess five of the chemicals most frequently found in it. Still, teens may buy it online and in some convenience stores and tobacco shops. About 11 percent of 12th graders admitted using it in the past year. Cough Medicine Each year, about five of every 100 high school seniors take cough medicine not to treat a cold, but to get high. Most often, they seek out the cough suppressant dextromethorphan (DXM). More than 120 over-the-counter cough and cold medicines contain it. At high doses—up to 1,500 milligrams, far more than the 15 or 30 milligrams recommended to treat coughs—DXM can cause the same types of out-of-body experiences as powerful hallucinogens like ketamine or PCP. Teens who abuse DXM risk life-threatening accidents while under the influence, as well as panic attacks, severe high blood pressure, and coma. Prescription Drugs When used properly, prescription medications can treat a wide variety of illnesses and injuries. But about 15 percent of teens use them incorrectly, either taking drugs meant for someone else or not using them as directed. Three types of prescription drugs are commonly abused: narcotics, amphetamines and other stimulants, and tranquilizers or depressants. Narcotics The most popular narcotics are Vicodin, used by 8.1 percent of 12th graders in the past year, and OxyContin, used by 4.9 percent. They're prescribed to relieve pain, but they also reduce anxiety and tension. Teens who abuse them risk nausea, vomiting, slowed breathing, addiction, and even death. Amphetamines Amphetamines are types of stimulants—drugs that speed up the body's systems. About 8 percent of 12th graders misused them in the past year. And 6.5 percent abused Adderall, an amphetamine used to treat attention deficit hyperactivity disorder (ADHD). Teens may think these drugs help them concentrate and feel alert. However, high doses of amphetamines or other stimulants can cause dangerous spikes in body temperature, irregular heartbeat, heart failure, and seizures. Tranquilizers Also called depressants, these drugs are used to treat conditions such as anxiety, insomnia, and seizures. Teens take high doses of medications like Xanax and Valium in search of feelings of euphoria. In the short term, abusing depressants can cause amnesia, confusion, and impaired judgment. Over time, teens can become dependent on them. Other effects include poor coordination, weakness, low blood pressure, blurred vision, and slowed breathing. And when depressants are combined with other drugs or alcohol, the results can be fatal. Key Takeaways A recent government survey found that the drugs teens abuse most include marijuana, cough medicine—particularly the cough suppressant dextromethorphan—and prescription drugs. Teens frequently acquire recreational drugs directly from the family medicine cabinet. Synthetic marijuana—also known as spice—is becoming more popular. Three types of prescription drugs are commonly abused: narcotics, amphetamines and other stimulants, and tranquilizers or depressants.