The term drug half life is used to describe the duration of time which is required for the trace concentration of a drug within the body to be reduced by one half. Scientists and other drug experts typically consider drug half life in relation to the amount of the substance found in the body’s plasma, which is the component of blood containing blood cells. This means that an assessment of a drug half-life is dependent on how rapidly the drug is eliminated from the plasma. The removal of a drug from the plasma is completed through a process known as ‘clearance’ and the distribution of the drug throughout the various bodily tissues is referred to as the volume of distribution. Each of these pharmacokinetic parameters is critical to any attempt in determining the drug half life of a particular substance. Every drug, whether illicit or legally obtained, has its own unique drug half life which can be used to determine if a person has ingested the drug recently.

The drug half life of commonly used drugs is as follows: Frequent users of marijuana face a drug half life of 10 days, while for infrequent users the rate drops to 1.5 days. The drug half life of cocaine has been found to be within 60 to 90 minutes, while methamphetamines have a drug half life of 15-20 hours. The prescription painkiller hydrocodone, commonly called Vicodin, has a drug half life of 4 to 6 hours, while the anxiety drug Xanax has a drug half life of 16 hours. Knowing the drug half life of a particular illicit substance is crucial when using drug testing kits to assess if someone has been using and abusing drugs. When you can ascertain exactly how long traces of a drug remain in the subject’s body, it is much easier to determine which testing option you should use. When testing for substances with a shorter drug half life, the best option is a urinalysis drug test which can be administered quickly and easily. If you are trying to determine a pattern of past drug use, with substances which have a longer drug half life, you should use the hair follicle drug test because it can detect traces of drugs up to 3 months after they were last used.