TLC screening procedures are recommended for the detection of counterfeit drugs. Numerous studies have demonstrated the multiple uses of these methods. They can be employed for the identification of drug substances, the estimation of drug substance content and the detection of related substances which could be regarded as impurities. TLC procedures are more specific and selective than WHO basic tests for the identification of drug substances (see section 9.2) and are also subject to less interference by excipients.

A counterfeit product may contain the correct active ingredients but in amounts other than those declared. In response to effective anticounterfeit measures, counterfeiters have often introduced small quantities of the genuine pharmaceutically active substances into the dosage forms. This gives positive identification results and in this way counterfeiters attempt to foil or confound the process of detection. In such cases, the basic tests are inadequate; TLC procedures are therefore preferred, as they are capable of giving semi-quantitative information on the active ingredient and also on any related substances in the dosage forms.