Can the length of time you last used be determined by hair follicle test?

Yes, a hair follicle test can provide an indication of drug use over an extended period, typically up to 90 days. The test analyzes the presence of drug metabolites in the hair, which grow at a rate of about half an inch per month. However, it cannot pinpoint the exact date of last use or the frequency of use, only the general timeframe in which drug use occurred.