how far back can a hair drug test go
A hair drug test, also known as a hair follicle test, can detect the presence of certain substances in the hair shaft for a period of several months. The length of time that a hair drug test can detect substances depends on several factors, including:
- Hair length: The longer the hair, the longer the detection period. Typically, a hair sample of 1.5 inches (3.8 cm) can detect substances for up to 3 months, while a sample of 3 inches (7.6 cm) can detect substances for up to 6 months.
- Hair growth rate: Hair grows at an average rate of 0.5 inches (1.3 cm) per month. Therefore, a hair sample can detect substances for a period of several months, depending on the growth rate.
- Substance type: Different substances have different detection periods. For example, marijuana can be detected for up to 3 months, while cocaine and opioids can be detected for up to 6 months.
- Test sensitivity: The sensitivity of the test can also affect the detection period. More sensitive tests can detect smaller amounts of substances, which can increase the detection period.
Here are some general guidelines for the detection periods of common substances in hair:
- Marijuana: 1-3 months
- Cocaine: 2-6 months
- Opioids: 2-6 months
- Amphetamines: 2-6 months
- Benzodiazepines: 1-3 months
- Barbiturates: 1-3 months
It’s essential to note that hair drug tests are not foolproof and can be affected by various factors, such as:
- Hair dye: Some hair dyes can affect the test results.
- Hair treatments: Certain hair treatments, such as bleaching or perming, can damage the hair shaft and affect the test results.
- Contamination: Hair can be contaminated with substances from the environment, which can affect the test results.
Overall, a hair drug test can detect substances for a period of several months, but the exact detection period depends on various factors.
