Codeine is a sleep-inducing painkiller medicine derived from morphine. Mice studies by researchers at University of Toronto have revealed that nicotine gives brain more codeine relief, putting smokers at a higher risk for addiction.
The research team observed that nicotine use over time increases the speed that codeine is converted into morphine within the brain, by increasing the amount of a specific enzyme. They found that smokers' brains are being primed for a bigger buzz from this common pain killer, which could put them at a higher risk for addiction, and possibly even overdose.
Researcher Rachel Tyndale said, "Researchers have known for some time that codeine was metabolized in the liver, but they've now discovered that this is also happening within the brain itself. Chronic nicotine use, or smoking, increases the amount of an enzyme that converts codeine into morphine within the brain, increasing pain relief. This may also make you more prone to addiction as the faster a drug gives you a high, the easier it is for you to learn the behavior and become addicted."
The study findings are part a new way of seeing the brain's role when it comes to drugs and toxins. Tyndale said, "Instead of a passive target with receptors idly waiting for drugs, the brain is actually playing a much more active role than was previously thought. Enzymes in the brain are busy breaking down, or ramping up, the effect of drugs and other substances. Understanding these enzymes and our genetic variation affecting our brain's metabolism could help explain why people react differently to drugs and toxins, and even why certain people are more susceptible to complex diseases like Parkinson's."
The study is published in Neuropsychopharmacology.