how far can a drug test go back with hair

A hair follicle drug test can detect the presence of certain substances in the hair shaft 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. However, if the hair is longer, the detection window can extend up to 6-12 months or even longer.
2. Type of substance: Different substances have different detection windows. For example:

   • Marijuana: 7-90 days
   • Cocaine: 7-120 days
   • Opiates: 7-90 days
   • Amphetamines: 7-90 days
   • PCP: 7-120 days

3. Frequency of use: The more frequently a substance is used, the more likely it is to be detected in the hair.
4. Sensitivity of the test: The sensitivity of the test can also impact the detection window. More sensitive tests can detect smaller amounts of a substance, which can extend the detection window.

Here’s a general guideline for the detection window of a hair follicle test:

• 1-3 months: Short-term use (e.g., a single use)
• 3-6 months: Moderate use (e.g., occasional use)
• 6-12 months: Long-term use (e.g., regular 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 specific test used.