Drug injection taking drugs, injection is favoured by some people as the full effects of the drug are experienced very quickly, typically in five to ten seconds. It also bypasses first-pass metabolism in the liver, resulting in higher bioavailability and efficiency for many drugs (such as morphine or diacetylmorphine/heroin; roughly two-thirds of which is destroyed in the liver when consumed orally) than oral ingestion would. The effect is that the person gets a stronger (yet shorter-acting) effect from the same amount of the drug. Drug injection is therefore often related to substance dependence. In a recreational context, the shorter, more intense "high"
Drug tolerance of intoxication when drinking even very small amounts of alcohol. Drug tolerance should not be confused with drug tolerability, which refers to the degree to which overt adverse effects of a drug can be tolerated by a patient. Tachyphylaxis is a subcategory of drug tolerance referring to cases of sudden, short-term onset of tolerance following the administration of a drug. Pharmacodynamic tolerance begins when the cellular response to a substance is reduced with repeated use. A common cause of pharmacodynamic tolerance is high concentrations of a substance constantly binding with the receptor, desensitizing it through constant interaction. Other possibilities include