Dextromethorphan, or DXM, a common active ingredient found in many over-the-counter cough suppressant cold medicines, is used as a recreational drug and entheogen for its dissociative effects. Street names include Brownies, Dextro, Drix, Gel, Groove, Lean, Mega-perls, Poor man's ecstasy, Poor man's PCP, Red devils, Robo, Rojo, Rome, Skittles, Sizzurp, Triple Cs, reds, Sky and Velvet.

It has almost no psychoactive effects at medically recommended doses. However, dextromethorphan has powerful dissociative and euphoric properties when administered in doses well above those considered therapeutic for cough suppression. Recreational use of DXM is sometimes referred to in slang form as "robo-tripping" or "skittling", whose prefix derives from the Robitussin brand name, or "Triple Cs", which derives from the Coricidin brand whose tablets are printed with "CC+C" for "Chest Congestion and Cough". However, this brand presents additional danger when used at recreational doses due to the presence of chlorpheniramine (antihistamine).

In over-the-counter formulations, DXM is often combined with acetaminophen (paracetamol, APAP) to relieve pain; however, to achieve DXM's dissociative effects, the maximum daily therapeutic dose of 4000 mg of APAP is often exceeded, potentially causing acute or chronic liver failure, making abuse and subsequent tolerance of products which contain both DXM and APAP potentially fatal.

An online essay first published in 1995 entitled "The DXM FAQ" described dextromethorphan's potential for recreational use, and classified its effects into so-called plateaus. Each plateau is categorized depending on how many milligrams of DXM are ingested, each featuring varying or more intense effects. The defined number of plateaus differs depending on the source, but the generally agreed-upon number is 4 or 5.

Owing to its recreational use, many retailers in the US have moved dextromethorphan-containing products behind the counter so that one must ask a pharmacist to receive them or be 18 years (19 in New York and Alabama, 21 in Mississippi) or older to purchase them. Some retailers also give out printed recommendations about the potential for abuse with the purchase of products containing dextromethorphan.

At high doses, dextromethorphan is classified as a dissociative general anesthetic and hallucinogen, similar to the controlled substances ketamine and phencyclidine (PCP). Also like those drugs, dextromethorphan is an NMDA receptor antagonist. It generally does not produce withdrawal symptoms characteristic of physical dependence-inducing substances, but cases of both psychological dependence and physical dependence have been reported in the past, although physical dependence is usually only seen in cases of heavy abuse. Due to dextromethorphan's selective serotonin reuptake inhibitor-like action, the sudden cessation of recreational dosing in tolerant individuals can result in mental and physical withdrawal symptoms similar to the withdrawal from SSRIs. These withdrawal effects can manifest as psychological effects, including depression, irritability, cravings, and as physical effects, including lethargy, body aches, and a sensation of unpleasant tingling, not unlike a mild "electric shock".

Dextromethorphan's effects have been divided into four plateaus.

Also, a marked difference is seen between dextromethorphan hydrobromide, contained in most cough suppressant preparations, and dextromethorphan polistirex, contained in the brand name preparation Delsym. Polistirex is a polymer that is bonded to the dextromethorphan that requires more time for the stomach to digest it, as it requires that an ion exchange reaction take place prior to its dissolution into the blood. Because of this, dextromethorphan polistirex takes considerably longer to absorb, resulting in more gradual and longer lasting effects reminiscent of time-release pills. As a cough suppressant, the polistirex version lasts up to 12 hours. This duration also holds true when used recreationally.