A hair test report usually hands you a verdict for each drug, positive or negative, rather than a measurement. Reading it well comes down to knowing what that verdict can and can’t prove about you. Hair holds a long, rough record of exposure, which makes it good at showing a pattern and poor at pinning down a single day or dose. The biggest open question is telling drug use apart from drug that reached the hair from outside, and how well labs manage that depends on the drug.1National Institute of Justice. Detecting Drugs in Hair: Is It Drug Use or Environmental Contamination?
What Positive and Negative Mean on Your Report
Every hair sample goes through a quick screening test first, and anything that flags is retested with a more precise confirmation test.2BSCG. How to Read Hair Follicle Test Results and Levels Each drug has a cutoff, a set amount below which the lab reports negative even if some drug is present.3Banned Substances Control Group. How to Read Hair Follicle Test Results and Levels A positive requires the drug to pass the cutoff on both the screen and the confirmation.4BSCG. How to Read Hair Follicle Test Results and Levels A flag on the screen alone that fails confirmation is reported as negative.5BSCG. How to Read Hair Follicle Test Results and Levels
If you’re told only that a screen was “non-negative” or “presumptive,” that is not yet a final positive. Ask whether the result you were given is the final confirmed one.
On the report itself, each drug or drug group usually sits on its own line with a result beside it: positive, negative, or sometimes “not detected.” The cutoff may be printed next to each drug. Labs generally tell employers and other outside parties only whether a result is above or below the cutoff, not an exact amount.6Banned Substances Control Group. How to Read Hair Follicle Test Results and Levels If a number does appear, it is often the cutoff, not your own level.
A negative doesn’t mean zero drug, only less than the cutoff. Light or one-time use can leave levels under the cutoff and still read negative.
Cutoff Levels for Common Drugs
Hair results are measured in pg/mg, picograms of drug per milligram of hair, a tiny amount measured against a small snippet.7Hair Drug Testing And Analysis. Hair Follicle Test Results Levels Chart, What pg/mg Means Cutoffs are set by regulators and industry agreement, not by the lab you happened to use.8BSCG. How to Read Hair Follicle Test Results and Levels Typical values look like this:
- Marijuana: about 1 pg/mg on the screen and 0.1 pg/mg on confirmation, which looks for a specific breakdown product.9BSCG. How to Read Hair Follicle Test Results and Levels
- Cocaine and its breakdown product: 500 pg/mg for both screen and confirmation at one large U.S. lab.10Quest Diagnostics. Hair testing certifications & cutoff levels
- Methamphetamine, amphetamine, and MDMA (ecstasy): 500 pg/mg for both steps at the same lab.11Quest Diagnostics. Hair testing certifications & cutoff levels
- Opiates such as codeine and morphine: often 200 pg/mg.12BSCG. How to Read Hair Follicle Test Results and Levels
- Other stimulants and PCP: generally set somewhere between 200 and 500 pg/mg depending on the lab.13BSCG. How to Read Hair Follicle Test Results and Levels
Marijuana’s cutoff looks so much lower because its breakdown product enters hair in far smaller amounts than cocaine or meth does. A small number on a marijuana line is not a sign of light use compared with other drugs.
Because cutoffs range between labs, the same sample could fall on different sides of the line at two labs. Many websites post charts that claim to rank levels as light, moderate, or heavy use. Those are not lab standards, and your report won’t use them. Rely on the cutoff printed on your own report.
The drugs tested also depend on the program, such as an employer’s policy, a court order, or a custody agreement. A five-drug panel and a wider panel will give different reports even when the same hair is tested. Check which drugs your order actually covered, because only those lines carry a result.
What the Number Can and Cannot Tell You
A level shows how much drug was deposited in the hair over the period tested.14Hair Drug Testing And Analysis. Hair Follicle Test Results Levels Chart, What pg/mg Means There is no accepted method to turn it into a dose, a count of times used, or a date.15Hair Drug Testing And Analysis. Hair Follicle Test Results Levels Chart, What pg/mg Means The reason is that how much drug ends up in hair varies widely between people, including by hair color. In one study of people given the same codeine doses, black hair held about 1,429 pg/mg while red hair held about 69 pg/mg.16PubMed. The effect of hair color on the incorporation of codeine into human hair At a 200 pg/mg cutoff, everyone with black hair tested positive and everyone with blond or red hair tested negative after the same use.17PubMed. The effect of hair color on the incorporation of codeine into human hair
The pigment that colors hair is a main place drugs like cocaine bind. Darker hair has more of it, so it can hold more drug.
For the same reason, a bigger number is not a bigger habit. A high level can come from moderate use in someone whose hair binds drug readily, while heavy use in someone else can give a lower level. Some testers will release the measured amount on request, but it won’t settle arguments about how heavy or recent use was.
Nor can a number give a date. Hair shows the drug was deposited somewhere in the window, not on which day. A single use and repeated use can both end up above the cutoff, and the number cannot separate them.
Use Versus Contamination
Drugs reach hair from the blood, from sweat and scalp oil, and from the surrounding air or surfaces.18National Institute of Justice. Detecting Drugs in Hair: Is It Drug Use or Environmental Contamination? So drug on your hair doesn’t automatically mean drug passed through your body.
Labs try to tell the difference in a few ways. They wash the hair before testing to strip off outside contamination.19Quest Diagnostics. Frequently asked questions Hair drug testing They look for metabolites, the breakdown products the body makes only when it processes a drug.20PubMed. Differentiation between consumption and external contamination when testing for cocaine and cannabis in hair samples Cutoffs are also set partly to screen out small amounts from the environment.21Choice DNA. Hair Follicle Test Results Levels Chart (pg/mg) & How to Read It None of this is airtight. In one comparison of five labs, cocaine powder rubbed onto hair still produced the same breakdown products seen in users.22PubMed. Performance of Hair Testing for Cocaine Use-Comparison of Five Laboratories Using Blind Reference Specimens Standard checks don’t fully rule out cocaine contamination.23PubMed. Performance of Hair Testing for Cocaine Use-Comparison of Five Laboratories Using Blind Reference Specimens
Exposure matters more for some drugs than others. Smoked drugs such as cannabis and crack cocaine put particles and residue in the air that can settle on hair. Hair that is oily or sweaty can hold onto that residue more easily.
Cannabis is the hardest case. Even a single short exposure to cannabis smoke left washed hair with levels typical of users.24PubMed. Analysis of Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) on hair after single and repeated short in vivo passive exposures to low- and high-Δ9-THC-cannabis Finding cannabis in hair is therefore not proof that someone used it.25PubMed Central. Finding cannabinoids in hair does not prove cannabis consumption Swallowed cannabis may not show in hair at all.26PubMed Central. Finding cannabinoids in hair does not prove cannabis consumption
Some websites say shampoos, ibuprofen, or diet pills cause false positives, but those claims lack strong support. Confirmation testing identifies the exact drug, so a cold medicine is not reported as meth. One real concern is that certain oil-free styling products can make hair absorb drugs from outside more easily.
If you think contamination explains your result, tell the reviewer where and when you were around the drug. Name people you live with who use.
How Dye, Bleach, and Treatments Affect Results
Dyed or bleached hair usually holds 40 to 60% less drug than untreated hair.27PubMed. Influence of the cosmetic treatment of hair on drug testing Dyes and bleach open up and damage the hair’s outer layer, letting some trapped drug escape. Bleaching lowers levels more than dyeing, and more damaged hair loses more.28PubMed. Influence of the cosmetic treatment of hair on drug testing
Even so, in routine testing, dyed and bleached hair turned up positive about as often as untreated hair.29PubMed. Utility of coloured hair for the detection of drugs and alcohol Cutoffs are low, so removing half the drug can still leave a level above them. Only someone with a level already near the cutoff has a realistic chance of being pushed below it. Coloring your hair is not a reliable way to get a negative. Testers often note visible treatment, and some ask for body hair instead.
If you colored your hair before the test, tell the collector so it can be noted. Deliberate tampering can be treated as a refusal in workplace testing.
Alcohol hair tests behave differently. Some check for an alcohol breakdown product, and bleaching cut its levels by about 80% and dyeing by about 63%.
What Time Period Your Result Covers
Head hair grows about half an inch a month.30Testing.com. Hair Follicle Drug Test The usual sample of about 1.5 inches cut near the scalp reflects roughly three months.31PubMed Central. Hair Analysis and its Concordance with Self-report for Drug Users Presenting in Emergency Department That is an estimate built from average growth, not from your own hair. Growth ranges widely between people, from about 0.6 to over 3 cm a month.32Agency for Toxic Substances and Disease Registry. Hair Analysis Panel Discussion Faster growers cover a shorter span in 1.5 inches, and slower growers cover a longer one, so “about three months” is a range, not a fixed date.
Very recent use won’t show. Hair takes about a week to grow out of the scalp, and the sample is cut at the scalp. Drug taken in roughly the last week is still in hair below the skin and not in the cut sample. A negative hair result therefore does not rule out use from last week. Body hair grows in longer cycles, so a body hair test covers a longer, less certain window.33PubMed Central. Hair Analysis and its Concordance with Self-report for Drug Users Presenting in Emergency Department
Labs can cut hair into sections to show roughly which months contained drug. But drug can spread along the hair through sweat and oil and appear in months with no use, so month-by-month claims deserve caution.
After stopping use, new hair grows in clean. Older drug-containing hair stays on the strand until it grows out past the cut length, so a sample taken near the scalp clears after about three months.
How the Sample Is Collected
The collector cuts about 100 milligrams of hair, roughly 90 to 120 strands, at the scalp.34Labcorp. Hair Follicle Drug Testing: Process & Benefits Cutting at the scalp ties the sample to the most recent months, which is what the time window assumes.
The hair is then sealed in foil and logged on chain-of-custody forms before shipping.35Labcorp. Hair Follicle Drug Testing: Process & Benefits Chain of custody is a paper trail recording who held the sample and when, from collection through the lab. Errors in that paperwork, such as gaps or unsigned handoffs, can be grounds to question a result.
During collection, make sure the form has your correct name and ID. Watch the sample being sealed, and keep your copy of the custody form.
What to Do If You Disagree With a Positive
In workplace testing, a Medical Review Officer (MRO), an independent doctor, reviews confirmed positives before your employer sees them.36Psychiatrist Expert Witness. What is a Medical Review Officer? Drug testing & Labs – Psychiatrist Expert Witness That gives you a chance to offer a medical explanation such as a prescription. Prescribed opioids like codeine will confirm positive, so a prescription is the key evidence.
Expect a call from the review doctor asking about medicines and prescriptions. Have prescription bottles or pharmacy records ready. Be honest, because they can only excuse what you document. They decide whether a legitimate medical explanation exists and can change a result to negative if a valid prescription explains it. They do not weigh claims like secondhand exposure the same way, and may still report a positive.
Workplace programs typically give a short window to respond after the review doctor contacts you. Missing it can mean the positive is reported as it stands, so return calls promptly and ask what the deadline is.
To push further, ask whether a portion of the sample was saved for another lab. Request the actual measured level and any wash results. For cannabis or cocaine, ask whether contamination checks were run.
U.S. courts generally accept hair results as evidence.37PubMed. Judicial acceptance of hair tests for substances of abuse in the United States courts: scientific, forensic, and ethical aspects Their weight can still be challenged over unresolved scientific issues such as contamination.38PubMed. Judicial acceptance of hair tests for substances of abuse in the United States courts: scientific, forensic, and ethical aspects In court cases, a lawyer may hire an independent toxicologist.