How far does a swab drug test go back?

Not medical advice: Swab tests, also called “spit tests” or “saliva tests”, can only go back as far as very recent drug use, which is about 24 to 48 hours in the past. They do not check for inhalants or alcohol. The presence or the absence of a specific drug like heroin can’t be tested for either. Swab tests only indicate the use of “parent drugs” like methadone, benzodiazepines, phencyclidine, THC (marijuana), opiates, cocaine, methamphetamines, and amphetamines.

Swab tests are currently making headlines because of schools that want to test students who are suspected of abusing drugs. The school committee for Westborough, Massachusetts schools just voted to rescind a policy that would allow staff to test students for illicit prescription drug use without the permission of parents.