At Cansford Labs, we often hear confusion around what a negative or positive drug
test really means, especially with hair testing. A common assumption is: “I’ve stopped
using drugs, so my test should be negative.” On the surface, that makes sense. In
reality it’s more complex, and it’s understandable that unexpected results can be
frustrating.
Take a recent example: a donor who stopped using ketamine at the start of February
was surprised to see a positive result in August. The test covered mid-March onwards,
and the donor believed that abstaining would guarantee a clean result. Hair testing,
however, doesn’t work that way.
Why hair testing is different
Hair testing doesn’t show current use, it shows historical use. Drugs enter the body
and are deposited into the hair follicle. As hair grows, it keeps a record of substances
used during that period. Even after someone stops using, the hair that grew during the
time of use can still show traces for months.
By contrast, urine and saliva tests detect recent use, usually within hours to a few
days. They’re ideal for spotting current intoxication or very recent consumption. Hair
testing is designed to show patterns of use over time, making it especially valuable in
legal, workplace, and safeguarding contexts.
Abstinence doesn’t always mean a “negative” result
Stopping drug use is a positive and important step, but it doesn’t instantly erase the
evidence from hair. Depending on when the substance was last used and how fast the
hair grows, traces can remain for months.
That doesn’t mean the test is unreliable. Hair testing is highly accurate, but it’s just
designed to track patterns rather than give a snapshot of a single moment. Each
person acts as their own control, so we can identify decreases or increases in
consumption over time. Even if a substance is still detectable, the overall trend can
show reduced, increase or maintained use, providing a clearer picture of use.
Learning more
We know drug testing can feel complicated, especially if it’s your first time. That’s why
we aim to help you understand the science before testing takes place, not after.
In our resources section, you’ll find downloadable guides explaining different testing
methods.
