how far back can a hair drug test show
A hair drug test, also known as a hair follicle test, can detect the presence of certain substances in the hair shaft for a relatively long period of time. The detection window for a hair drug test depends on several factors, including:
- Length of hair: The longer the hair, the longer the detection window. Typically, a hair sample of 1.5 inches (3.8 cm) can detect substance use for the past 90 days.
- Growth rate of hair: Hair grows at an average rate of 0.5 inches (1.3 cm) per month. This means that a hair sample can detect substance use for a period of time that is proportional to the length of the hair.
- Type of substance: Different substances have different detection windows. For example, marijuana can be detected for up to 90 days, while cocaine and opioids can be detected for up to 6 months.
Here are some general guidelines for the detection windows of common substances in a hair drug test:
- Marijuana: 30-90 days
- Cocaine: 30-180 days
- Opioids: 30-180 days
- Amphetamines: 30-90 days
- Methamphetamine: 30-90 days
- Benzodiazepines: 30-90 days
- Barbiturates: 30-90 days
Keep in mind that these are general estimates, and the actual detection window may vary depending on individual factors, such as the amount and frequency of substance use, as well as the sensitivity of the testing method.
It’s also worth noting that hair drug tests can detect substance use for a longer period of time than other types of tests, such as urine or saliva tests, which typically have detection windows of a few days to a week.
