Dextromethorphan, commonly called DXM, is an OTC cough suppressant and is available as a tablet or a liquid. According to the National Capital Poison Center, recreational abuse of this drug has become more common and accounts for about 6,000 hospital emergency department visits each year. Large doses can cause euphoria, distortions of color and sound, and out-of-body hallucinations that last up to 6 hours.¹ Some other dangerous side effects include impaired judgment, vomiting, loss of muscle movement, seizures, blurred vision, drowsiness, shallow breathing, and a fast heart rate. DXM is also addictive and can cause withdrawal symptoms, including depression and difficulty processing thoughts, when the drug is stopped.
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DXM is the active ingredient in more than 100 OTC cough and cold medicines, such as Robitussin and NyQuil. These products commonly contain one or more medicines to treat symptoms such as pain, congestion, and a runny nose. To enhance the effects of DXM, some teens combine other substances, such as alcohol or other OTC medicines. For example, Coricidin HBP Cough and Cold includes both DXM to treat a cough and an antihistamine (chlorpheniramine) to treat a runny nose. When DXM is taken in large quantities and in combination with other medicines, serious injury and even death have occurred.¹

Reference

1) Department of Justice/Drug Enforcement Administration. Drug Fact Sheet. (April 2020).   

OTC caffeine tablets or capsules such as NoDoz or pain relievers with caffeine are often abused for the buzz or jolt of energy they seem to provide. If these tablets or capsules are taken with high caffeine energy drinks, the effects are felt even quicker. Large doses of caffeine can cause serious dehydration, gastric reflux disease, panic attacks, and heart irregularities that have occasionally been linked to accidental deaths, particularly in those with an underlying heart condition.

In large doses, diet medicine can create a mild buzz. But misuse of diet medicine can also signal a serious eating disorder. Abuse of diet medicine often starts with taking just a few tablets or capsules in order to lose weight. But these OTC medicines can be highly addictive. Although the US Food and Drug Administration (FDA) has banned several of the most dangerous stimulants commonly found in OTC diet medicines—phenylpropanolamine, ephedrine, and ephedra—other ingredients in these OTC products can also be dangerous. To cite an example, bitter orange is a common ingredient that acts much like ephedrine.¹ It can cause nervousness and tremor, rapid and irregular heartbeat, high blood pressure, stroke, heart failure, and death. Many other diet medicine ingredients cause digestive problems, hair loss, insomnia, anxiety, irritability, extreme paranoia, blurred vision, kidney problems, and dehydration. Furthermore, even the most "natural" diet preparations can have serious side effects when misused, particularly those containing ma huang (ephedra).

Reference

1) WebMD. Bitter orange - uses, side effects, and more. Natural Medicines Comprehensive Database Consumer Version. Therapeutic Research Faculty 2020.

Like diet medicines, some teens and young adults also abuse OTC laxatives (e.g., Dulcolax, Senokot) and herbal diuretics (water pills), including uva ursi, goldenseal, dandelion root, rose hips, and others, to lose weight. Laxatives and herbal diuretics can cause serious dehydration and life-threatening loss of important minerals and salts that regulate the amount of water in the body, acidity of the blood, and muscle function.

Motion sickness medicine that contains dimenhydrinate (Dramamine Original Formula) or diphenhydramine (Benadryl), if taken in large doses, can cause someone to feel high and have hallucinations similar to street drugs. The dose needed to cause these symptoms varies according to body weight and tolerance. Some teens and adults have taken as many as 40 tablets of Dramamine, for example, to experience the desired high. Extremely high doses of Dramamine have caused dangerous irregular heartbeats, coma, heart attacks, and death. Long-term abuse can cause depression, liver and kidney damage, memory loss, eye pain, itchy skin, urine retention, and abdominal pain.

OTC sexual performance medicines (e.g., Kaboom Action Strips, EreXite), often purchased via the Internet or at gas stations and truck stops, are sometimes abused by teens and adults to counteract the negative effects of alcohol on sexual performance.¹ These medicines can cause heart problems, especially when combined with alcohol or when taken in large doses.

Reference
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1) TeenHelp.com. Types of OTC drugs abused (2013).

This nasal decongestant and stimulant is found in many cold medicines. Its similarity to amphetamines make it a highly sought out drug which is then used to make the illegal drug methamphetamine. The medicine has also been taken as a stimulant to cause an excitable, hyperactive feeling. Abuse may be less common with pseudoephedrine than with other OTC medicines due to a federal law requiring it to be kept behind the pharmacy counter, limiting the purchase quantity, and requiring photo identification prior to purchase. However, people have taken pseudoephedrine to lose weight, and athletes have misused the medicine to increase their state of awareness and to get them "pumped up" before a competition. Dangerous side effects include heart palpitations, irregular heartbeats, and heart attacks. When combined with other drugs, such as narcotics, pseudoephedrine may trigger episodes of paranoid psychosis.

This is a combination of inexpensive herbs that are legally sold in tablet or capsule form and can be swallowed, snorted, or smoked to produce euphoria, increased awareness, and enhanced sexual sensations. Marketed as a "natural" high, the main ingredient is ma huang (ephedra), an herb banned in the United States but only when used  in dietary supplements. The product can be purchased at gas stations, health food stores, drug stores, music stores, nightclubs, and online. It is easy to overdose on the product because the dose needed for desirable effects varies. The adverse effects can be severe, including muscle spasms, increased blood pressure, seizures, heart attacks, strokes, and death.

Other herbal products are increasingly being abused for their stimulant, hallucinogenic, and euphoric effects. One example is salvia, which is ingested or smoked to experience a short-lived distortion of reality and hallucinations.¹ Users can experience severe anxiety, loss of body control, extreme psychosis, and violent behavior. They are also at risk for accidents and injuries that may result from an altered mental state. Some states have regulated the sale of salvia. Another example is nutmeg, which is eaten as a paste to experience giddiness, euphoria, and hallucinations. Nausea and vomiting set in within an hour. Hallucinations begin within 3 hours and can last for 24 hours or more. Effects such as blurred vision, dizziness, numbness, palpitations, low blood pressure, and rapid heartbeat may occur.

Reference

1) Richardson III WH, Slone CM, Michels JE. Herbal drugs of abuse: an emerging problem. Emerg Med Clin North Am. 2007;25(2):435-57.

Adults and teens have taken pain relievers like acetaminophen (Tylenol) and ibuprofen (Motrin) in doses higher than recommended not to get high but because they mistakenly believe the medicine will work faster.¹ They don't think of the side effects. They don't know that liver failure can happen with large doses of acetaminophen, and that stomach bleeding, kidney failure, and cardiac risks are heightened when taking large doses of ibuprofen.

Reference

1) TeenHelp.com. Types of OTC drugs abused (2013).