If you have a hair drug test coming up, you’re likely wondering just how far back it can see into your past. Unlike urine or saliva tests that measure recent use, a hair follicle test offers a much longer detection window. It’s a common choice for pre-employment screenings and legal cases precisely because of its ability to provide a historical record of substance use.
The standard timeframe that most labs look at is the 90 days prior to the test. This is because head hair grows at an average rate of about half an inch per month. For the test, a small sample of hair is cut close to the scalp, typically 1.5 inches in length. This 1.5-inch segment represents approximately three months of growth, giving a clear picture of any drug use during that period.
Factors That Can Extend the Detection Window
While 90 days is the standard, the detection period isn’t always set in stone. If you provide a longer hair sample, the lab can analyze a longer period. Some tests may use body hair, which grows at a different, often slower, cycle. Because of this, a body hair test might be able to detect substances used over the past year. It’s also important to know that hair tests are excellent at identifying patterns of repeated or habitual use rather than a single, isolated incident.
What the Test Can and Cannot Reveal
Hair follicle tests are highly effective at detecting a range of substances, including marijuana, cocaine, opiates, amphetamines, and PCP. However, they are not typically used to prove very recent use, such as within the last few days. It takes about 5-7 days for the hair containing drug metabolites to grow out from the scalp enough to be collected in the standard sample. This test provides a broader timeline, offering a history rather than a snapshot.
Preparing for a Hair Follicle Test
The most reliable way to prepare for a hair drug test is to abstain from any substance use. Because the test captures a long history, last-minute attempts to “clean” your hair are generally ineffective against professional laboratory procedures. Many detox shampoos on the market make bold claims but often fail to alter the test results, as the metabolites are embedded inside the hair shaft.
In summary, a standard hair drug test provides a reliable record of drug use for up to 90 days. Its long detection window makes it a powerful tool for organizations seeking a comprehensive look into an individual’s substance use history.