Poor drug metabolizer, lower dose requirements, higher risk for adverse side effects
References
Soyama A, Kubo T, Miyajima A, Saito Y, Shiseki K, Komamura K, Ueno K, Kamakura S, Kitakaze M, Tomoike H, Ozawa S, Sawada J: Novel nonsynonymous single nucleotide polymorphisms in the CYP2D6 gene. Drug Metab Pharmacokinet. 2004 Aug;19(4):313-9. [PubMed:15499201]
Sakuyama K, Sasaki T, Ujiie S, Obata K, Mizugaki M, Ishikawa M, Hiratsuka M: Functional characterization of 17 CYP2D6 allelic variants (CYP2D6.2, 10, 14A-B, 18, 27, 36, 39, 47-51, 53-55, and 57). Drug Metab Dispos. 2008 Dec;36(12):2460-7. doi: 10.1124/dmd.108.023242. Epub 2008 Sep 10. [PubMed:18784265]
The Human Cytochrome P450 (CYP) Allele Nomenclature Database [Link]