When Are You Safe From a Drug Test? The Lifespan of Weed in Your Hair

That moment of utter relaxation that accompanies peak stoned comes at a cost. Namely, after you’ve been asked to take a surprise drug test, and the 90 days of paranoia hits you harder than the hit did. Unfortunately, there’s not much you can do, except try not to reset the clock with another hit while you wait.

Here’s how your luscious locks give you away. When you ingest weed, whether through smoking, vaping, or eating, the active compounds in weed, cannabinoids, take a stroll through your bloodstream. One of their stops includes the blood vessels that feed your scalp. From there, compounds leftover from metabolizing THC enter a strand of your hair from the base, at the hair papilla, waiting to emerge from your scalp for detection.

Drug tests usually analyze samples of hair close to the scalp, from the freshest 1.5 inches. Hair grows about 0.5 inches per month, which makes three months, or 90 days, the average amount of time before that 1.5-inch chunk is THC-free.