Cocaine is a psychoactive alkaloid of the coca plant; it was originally used for local surgeries as an anaesthetic but has now become a recreational drug. Unlike amphetamines, which resemble the structural formula of dopamine and noradrenaline, cocaine has a similar structure to other synthetic sedatives. Cocaine is well absorbed when administered via the mucous membranes, the GI tract and IV route. Peak concentration happens within five minutes after intravenous injection, while the peak levels from smoking are usually reached within 60 minutes. Some cocaine is excreted in urine unchanged, the majority is metabolised into benzoylecgonine, ecgonine methyl ester, norcocaine and other metabolites. Although cocaine has a short half-life, the elimination half-life of the metabolites lasts longer. Studies also show that the half-life of cocaine may increase the longer it is used.
There are two main ways that heroin is metabolised; one of the ways is through the Hepatic First Pass. This is done via the removal of an acetyl group when taken orally. The other way is through injections. Heroin that is administered via this route will evade the Hepatic First Pass and will quickly cross the blood-brain barrier. This is because of the presence of an acetyl group that makes it more soluble to fat. Once, in the brain, the acetyl group is removed, and heroin is reduced to 3-monoacetylmorphine and 6-monoacetylmorphine.