Melanin and nicotine: A review of the literature.

The role of melanin in nicotine uptake and metabolism has received little attention. Because nicotine has been shown to accumulate in tissues containing melanin, exploring links between melanin and nicotine may provide additional clues to understanding smoking behavior and disease effects. To examine the scientific literature on the relationship between melanin and nicotine, we conducted a PubMed search. We also searched online archives of internal tobacco industry documents. We retrieved and reviewed 82 published research papers related to melanin and nicotine or melanin and metabolism of other drugs, and 150 relevant internal tobacco industry documents. The published literature suggests that nicotine may accumulate in human tissues containing melanin and this retention may increase melanin synthesis. Existing research on the relationship between melanin and nicotine lacks an adequate consideration of this relationship's potential impact, if any, on nicotine metabolism, level of nicotine dependence, and ability to quit smoking. Differential accumulation of nicotine in melanin-containing tissues could have implications for individuals with high levels of melanin.