Abuse of drugs has actually been measured in fingernails since 1984. However, the need to test for longer detection periods have given fingernail testing a new niche to fill.

Like hair, fingernails and toenails are composed of a hard protein called keratin. Drugs are incorporated into nails from the blood stream and remain locked in the nail as it grows in both length and thickness. Drugs enter the nail from the base as the keratin is formed and via the nail bed that extends under the full length of the nail.

Drugs can be identified in nail clippings 2-4 weeks following ingestion and can be detected up to 8 months after last usage. Fingernails grow approximately 3-5 mm per month, toenails grow at a much slower rate of 1 mm per month which means that drugs can possibly appear in toenail clippings over 1 year after ingestion.

Fingernail testing allows for testing up to 14 different drugs and most closely resembles hair testing regarding costs, drugs tested, methodology, and detectability periods.