A substance can be legal but may be banned in certain circumstances. For instance, an insurance company may test an insurance applicant for nicotine to verify the person's assertion that he or she is not currently using tobacco. In the case of prescription medications, the high addictive potential for certain medications makes drug testing important. In the case of some athletes, many of the prohibited substances are legal but have the potential to affect the athlete's performance. Athletes must exercise caution in their choices of medications as they are ultimately responsible for any substances detected in their bodies.
There are five primary color-tests reagents used for general screening purposes. The Marquis reagent turns into a variety of colors when in the presence of different substances. Dille-Koppanyi reagent uses two chemical solutions which turns a violet-blue color in the presence of barbiturates. Duquenois-Levine reagent is a series of chemical solutions that turn to the color of purple when the vegetation of marijuana is added. Van Urk reagent turns blue-purple when in the presence of LSD. Scott Test's chemical solution shows up as a faint blue for cocaine base.