October 16, 2015

Nicotine gives brain more pain relief from codeine, changing our view of the brain’s role in metabolizing drugs

(October 16, 2015)  According to new research, nicotine use over time increases the speed that codeine is converted into morphine within the brain, by increasing the amount of a specific enzyme. It appears 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.

“We’ve known for some time that codeine was metabolized in the liver, but we’ve now discovered that this is also happening within the brain itself,” Dr. Rachel Tyndale, senior scientist in the Campbell Family Mental Health Research Institute at the Centre for Addiction and Mental Health (CAMH), and University of Toronto pharmacology, toxicology, and psychiatry professor.

“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.”

These findings, published earlier this year in the peer-reviewed journal Neuropsychopharmacology, contribute to a new way of seeing the brain’s role when it comes to drugs and toxins. Instead of a passive target with receptors idly waiting for drugs, Dr. Tyndale has found that 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 disease.

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