What is the relevance of the OPRM1 A118G polymorphism to naltrexone for alcohol use disorder?

• A. It has no clinical relevance
• B. Carriers have a uniformly better response in all cases
• C. OPRM1 A118G is associated with altered mu-opioid receptor function
• D. It only affects pain management

Answer: (C)

The key idea is pharmacogenetics: a genetic variation in the mu-opioid receptor can change how this system works and, in turn, how a drug that targets it performs in alcohol use disorder. The A118G change in OPRM1 alters mu-opioid receptor function (for example, it can affect how endogenous opioids like beta-endorphin interact with the receptor). Because naltrexone blocks mu-opioid receptors to blunt the rewarding effects of alcohol, this genetic difference can influence treatment response. That’s why this polymorphism is described as being linked to altered receptor function and potentially to different treatment outcomes with naltrexone.

It isn’t that there’s no clinical relevance, nor that everyone with the variant responds better in every case, and it’s not limited to pain management—the finding specifically relates to how the reward system tied to alcohol and its pharmacologic blockade by naltrexone interact.