Influence of Pigmentation on the Codeine Content of Hair Fibers in Guinea Pigs

In a 1997 study involving seven tortoise shell guinea pigs, codeine was administered in their drinking water for three weeks. Analysis of hair samples collected before and after treatment showed that all hair fibers tested positive for codeine, with the highest drug content found in black hair samples. Non-pigmented hair showed the lowest drug concentrations, and reddish-brown fibers had less drug content than black hair samples from the same animal. The study concluded that eumelanins, not pheomelanins, are the key factor for codeine-melanin binding in hair. The study also suggested that the amount of drug intake could determine the impact of hair pigmentation on the analytical results.