The first studies measuring drugs in biological fluids were carried out to determine possible overdosing as part of the new science of forensic medicine/toxicology.
Initially, nonspecific assays were applied to measuring drugs in biological fluids. These were unable to discriminate between the drug and its metabolites; for example, aspirin () and sulfonamides (developed in the 1930s) were quantified by the use of colorimetric assays. Antibiotics were quantified by their ability to inhibit bacterial growth. The 1930s also saw the rise of pharmacokinetics, and as such the desire for more specific assays. Modern drugs are more potent, which has required more sensitive bioanalytical assays to accurately and reliably determine these drugs at lower concentrations. This has driven improvements in technology and analytical methods.