A hair follicle drug test typically detects drug use going back about 90 days (3 months). This is based on the standard practice of testing approximately 1.5 inches (3 cm) of hair closest to the scalp, as hair grows at about half an inch (1.25 cm) per month

. However, if longer hair samples are available, especially from slower- growing body hair, the detection window can extend up to 12 months. This requires testing longer hair segments (up to 12 cm) and often involves segmented analysis, where hair is divided into 3 cm sections to provide a timeline of drug use over the past year. This method is more complex and costly, and not all labs offer it

. In summary:

• Standard hair follicle test: Detects drug use within the past 3 months using 1.5 inches of scalp hair.
• Extended testing: Can detect drug use up to 12 months if longer hair samples are tested in segments.
• Body hair samples: May provide detection windows up to a year due to slower growth.

This makes hair follicle testing useful for identifying chronic or repeated drug use over time rather than very recent or occasional use

. Drugs commonly detected include cocaine, opioids, amphetamines, marijuana, PCP, benzodiazepines, and MDMA

. Note: Hair treatments like bleaching or dyeing, as well as sweat and environmental factors, can affect test results