How Long Do Drugs Stay in the Body?

Understanding Detection Windows in Hair, Nails, and Urine

When drug testing evidence is presented in family court, timing matters as much as detection. A result showing that a substance was found doesn’t necessarily prove recent use, or even deliberate use, yet those distinctions can have major implications in care proceedings.

That’s why understanding how long drugs stay in the body, and how different testing matrices tell different stories, is crucial for family lawyers, social workers, and local authorities alike.

Hair, Nails, and Urine: The Three Main Testing Matrices

Each sample type reveals a different timeframe of substance exposure. At AttoLife, we predominantly use head hair for drug testing analysis, or body hair when head hair is not available. In the instance where no hair is available, fingernails or toenails can be used.

Urine has the shortest detection window and is more commonly used for recent drug consumption in workplace or healthcare settings (like over at AttoSure), however Urine test results can be used in a court of law for recent infractions that have occurred in the last few days.

• Hair testing offers the longest detection window — typically up to 12 months per 12 cm of head hair, depending on growth rate. Segmental analysis can even show patterns of increasing or decreasing use over time.
• Body hair extends that window further (sometimes up to 12 months) but offers less precise dating.
• Nail testing provides a similar long-term overview — roughly up to six months retrospectively for fingernails and 12 months for toenails, and can be particularly useful when head or body hair is unavailable or chemically treated.
• Urine testing reflects very recent use, usually within 1–7 days, depending on the drug and the donor’s metabolism.

In short, hair and nail samples capture the story of use over time; urine captures only the most recent chapter.

If You’re Wondering How Long Drugs Stay in Your System…

You’re not alone. Questions like:
“How long does coke stay in your system?”
“How long does ketamine stay in your system?”
“How long does codeine last in the body?”

are among the most-searched drug-testing queries in the UK.

A toxicologist, however, might frame these differently — asking how long the metabolite (the compound your body breaks the drug into) remains detectable. For example:

• When people ask “how long does coke stay in your system,” a scientist looks for benzoylecgonine — the primary metabolite of cocaine.
• When people ask “how long does morphine stay in your system,” it may relate to heroin or codeine use.
• For “how long does ket stay in your system,” the answer depends on norketamine, ketamine’s breakdown product.

These metabolites last longer than the effects of the drug itself — meaning detection windows are often much longer than people expect. 

Typical Detection Windows

Substance	Hair (head)	Fingernails	Urine	Notes
Cocaine / Benzoylecgonine	Up to 12 months	Up to 6 months	1–3 days	Benzoylecgonine is stable and persists beyond intoxication
Cannabis (THC-COOH)	Up to 12 months	Up to 6 months	2–7 days (occasional), longer if chronic	Stored in body fat; slowly released
Codeine / Morphine	Up to 12 months	Up to 6 months	1–3 days	May appear from legitimate medication use
Ketamine / Norketamine	Up to 12 months	Up to 6 months	1–5 days	Detectable even after short-term use
Heroin / 6-MAM / Morphine	Up to 12 months	Up to 6 months	1–2 days	Rapidly metabolised but traceable via morphine markers

Will One Line of Cocaine Show Up on a Drug Test?

It’s one of the most common questions people ask — often phrased as:

“Will one line of coke show up on a drug test?”

“How much do you have to take to fail a drug test?”

“Will a small amount of ketamine stay in my system?”

The truthful answer is: it depends.

Detection isn’t simply about how much of a substance was used — it’s influenced by:

• Metabolism: Everyone breaks down drugs at a different rate. Factors such as age, weight, liver enzyme activity, hydration, and overall health all affect how quickly a substance leaves the body
• Time since use: Most drugs clear from urine within a few days, but metabolites (such as benzoylecgonine from cocaine) can linger longer, especially after repeated exposure.
• Testing matrix: A single event (like a single line of coke) might not appear in a hair or nail test if it was an isolated use and concentrations fall below laboratory detection limits. However, hair analysis can detect consistent or repeated use with high reliability.
• Hair treatments: Bleaching, dyeing, or chemical straightening can reduce detectable levels, though not always eliminate them.
• External contamination: Particularly relevant for cocaine, as surface contact (for example, handling banknotes or powder) can deposit the drug onto the hair.

Because of this, laboratories apply cut-off levels. These are scientifically established thresholds recommended by the Society of Hair Testing (SoHT) to distinguish likely ingestion from environmental exposure. In other words, a positive result isn’t triggered by trace contamination; it reflects drug or metabolite levels consistent with active use.
So while a single, small exposure might go undetected — especially in hair — it’s impossible to rely on that outcome. Testing is designed to identify genuine patterns of use, not to trap individuals for incidental contact.

Why Test Results Can Seem Confusing

Sometimes, a hair or nail result doesn’t align with lived experience. A person might say they’ve stopped using months ago, yet a segment of hair still tests positive.
There are valid scientific reasons for this:

• Segment length and growth rate: 1 cm of head hair roughly equals one month, but growth rates vary by person
• Historical use: Previous chronic drug users can present metabolites in new hair growth several months after last use.
• Metabolic differences: Slow metabolisers may retain metabolites longer.
• Environmental contamination: Cocaine in particular can appear from external contact unless confirmed with metabolite analysis.
• Bleaching, dyeing, or damage: May reduce concentration or complicate interpretation.

That’s why context and not just chemistry is vital in family-court evidence.

From “Presence” to “Proof”: The Importance of Interpretation

A detected result means the presence of a substance or its metabolite above a certain threshold (the cut-off level). But that doesn’t always equal misuse.
Legal practitioners should understand:

• Cut-off levels distinguish environmental exposure from active use.
• Abstinence periods (for example, several months drug-free) may still show residual traces in long-term matrices.
• Mixed-matrix results (hair + urine, or hair + nails) often provide the most reliable evidence.

Without careful interpretation, it’s easy to overstate or misrepresent what a test truly means.

Join Our Upcoming CPD Session

These complexities form the heart of AttoLife’s new CPD-accredited webinar:
Most Commonly Tested Drugs: Best Practices and Potential Pitfalls, 28 October 2025 – 2 pm

This session focuses on the three most commonly tested substances — cocaine, cannabis, and alcohol — and introduces the extended topic of the “big four” (cocaine, cannabis, ketamine, and heroin).

You’ll learn:

• How each substance appears across hair, nail, and urine tests
• What their presence really means
• How contamination, passive exposure, and metabolite interpretation affect reliability
• Practical strategies to strengthen court submissions

Register now to earn CPD points and gain deeper insight into how testing evidence stands up to scrutiny in family-law proceedings.

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