Melanin Binding
Definition
The non-covalent association of basic and lipophilic drugs (cocaine, opiates, amphetamines, nicotine) with melanin granules in the hair cortex. Pigmented (black, brown) hair retains substantially more drug than blonde or grey hair from the same dose, producing the well-known hair-colour bias in concentration readings.
- Mechanism
- Non-covalent binding to melanin granules in hair cortex
- Affected drugs
- Cocaine, opiates, amphetamines, nicotine
- Effect
- Pigmented hair retains more drug than blonde/grey hair
- Known limitation
- Hair-colour bias in concentration results
Common questions
How do labs correct for melanin binding when interpreting hair drug results?+
Some labs report results with caveats about hair colour or use segmental analysis and comparison to population reference ranges stratified by pigmentation, though a fully validated correction factor that removes the bias is not standard across the field.
Does melanin binding affect all drugs equally?+
No, basic, lipophilic drugs such as cocaine and amphetamines show strong melanin affinity and pronounced colour bias, while some other drug classes bind less to melanin, so the degree of bias depends on the specific compound's chemistry, not hair colour alone.
Related terms
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- Parent-to-Metabolite Ratio
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- Segmental Analysis
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