There are a variety of substance test methods available, but all rely on access to a biological sample like urine, blood, sweat or hair. There are five main categories of substances that are most commonly tested for, and they are cannabinoids, cocaine, opiates, amphetamines, and phencyclidine. Although there are many other types of drugs that people use, these five have gained prominence because they are specifically mentioned in the Substance Abuse and Mental Health Services Administration (SAMHSA) guidelines. Most drug assessments are capable of identifying all five so that just one sample can be used to identify the presence of multiple drugs. Companies that want to detect drugs that are not part of the SAMHSA 5 are still able to do so because there are a wide variety of substance test kits on the market.
In an effort to be as accurate as possible, the kits look for not only the drug, but also its metabolites. A metabolite is the leftover product of something once it has been metabolized. Identifying metabolites can prolong the amount of a time a drug can be detected in the body, because after traces of the drug itself have disappeared the metabolites linger.
Collecting urine for testing is the most common practice because it is inexpensive without sacrificing accuracy, and it is not intrusive. Saliva is useful for detecting recent use but is not as sensitive to cannabinoids as the other methods. A hair sample can detect use spanning months and sometimes even as long as a year ago. A blood sample provides the most accurate data but is also the most expensive to have processed. A substance test that uses sweat is gathered through the use of a patch that is worn for an extended period of time, but these are subject to inaccuracies if they are contaminated during that time period. Although each method has benefits and shortcomings, all of them are fairly accurate, and those that are performed on-site can be verified through laboratory processing for the most concise results.