how far back can a hair follicle drug test go

A hair follicle drug test can detect the presence of certain substances in the body for a longer period than other types of tests, such as urine or blood tests. The detection window for a hair follicle test depends on several factors, including:

1. Length of hair: The longer the hair, the longer the detection window. Typically, a 1.5-inch (3.8 cm) hair sample can detect substances used in the past 90 days.
2. Growth rate of hair: Hair grows at an average rate of 0.5 inches (1.3 cm) per month. This means that a 1.5-inch (3.8 cm) hair sample can detect substances used in the past 3-6 months.
3. Type of substance: Different substances have different detection windows. For example:

   • Marijuana: 7-90 days
   • Cocaine: 7-90 days
   • Opiates: 7-90 days
   • Amphetamines: 7-90 days
   • PCP: 7-90 days

4. Sensitivity of the test: The sensitivity of the test can also affect the detection window. More sensitive tests can detect smaller amounts of substances, which can increase the detection window.

In general, a hair follicle test can detect substances used in the past:

• 30-60 days for short-term use
• 60-90 days for moderate use
• 90 days or more for heavy or prolonged use

Keep in mind that these are general estimates, and the actual detection window may vary depending on individual factors, such as hair growth rate, metabolism, and the amount of substance used.