Table 1.

Assignment of likely codeine metabolism phenotypes based on cytochrome P450 2D6 diplotypes – data of Crews et al. (2012, 2014)

Likely phenotypea	Activity score	Genotype
Ultra‐rapid metabolisers (~ 1–2% of population)	> 2.0	An individual carrying more than two copies of functional alleles
Extensive metaboliser (~ 77–92% of population)	1.0–2.0	An individual carrying two alleles coding for a full or reduced function or one full function allele together with either one non‐functional or one reduced‐function allele
Intermediate metaboliser (~ 2–11% of population)	0.5	An individual carrying one reduced and one non‐functional alleles
Poor metaboliser (~ 5–10% of population)	0	An individual carrying no functional alleles

^aThe frequency estimates are based on data from Caucasians and may differ substantially for other ethnicities.