Hydrocodone or dihydrocodeinone is a semi-synthetic opioid derived from either of two naturally occurring opiates—codeine and thebaine. It is an orally active narcotic analgesic (pain reliever) and antitussive (cough suppressant). It is commonly available in tablet, capsule, and syrup form, and is often compounded with other, generally less effective non-opioid compounds such as paracetamol (also known as acetaminophen) or ibuprofen, often added both to discourage recreational use (as paracetamol can cause potentially fatal liver toxicity at high doses), and to provide a possible synergy of analgesic effects between hydrocodone and the non-opioid compounds present. The particular niche in which hydrocodone is most commonly used is as an intermediate centrally acting analgesic.

Hydrocodone presents much of the same side-effects as other opioids including euphoria, sedation and somnolence. Hydrocodone is one of the most common recreational prescription drugs in America, along with oxycodone. Recreational hydrocodone use is particularly prevalent among teenagers and young adults because of the drug’s widespread availability.

Many users of hydrocodone report a sense of satisfaction, especially at higher doses. A number of users also report a warm or pleasant numbing sensation throughout the body, one of the most well known effects of narcotics. Withdrawal effects may include, but are not limited to; severe pain, pins and needles sensation throughout body, sweating, extreme anxiety and restlessness, sneezing, watery eyes, fever, depression, and extreme drug cravings, among others. The presence of paracetamol in hydrocodone-containing products allegedly deters many users, at least in theory, from taking excessive amounts. However, some users will bypass this danger by using cold water extraction to extract and dispose of a portion of the paracetamol, taking advantage of the water-soluble element of the drug. It is not uncommon for users to have liver problems from consuming excessive amounts of paracetamol over a long period of time; taking 10,000 to 15,000 milligrams (10 to 15 grams) of paracetamol in a period of 24 hours typically results in paracetamol overdose and severe hepatotoxicity; doses in the range of 15,000–20,000 milligrams a day have been reported as fatal. It is this factor that leads many recreational users to use only single-entity opioids such as oxycodone. One of the major problems today with the illicit use of hydrocodone, especially in younger populations, is that users may not be aware that hydrocodone pills contain paracetamol.

Reference: http://en.wikipedia.org/wiki/Hydrocodone