Enantiomers are mirror-image molecules that have the same chemical formula but different spatial arrangements. In the case of opioids, there are two enantiomers: the right enantiomer (R-enantiomer) and the left enantiomer (S-enantiomer). The R-enantiomer is the more potent form of the opioid, and it is the form that is typically used in pain medication.

The body picks right opioid enantiomers because they have a higher affinity for the opioid receptors in the brain. Opioid receptors are proteins that are located on the surface of nerve cells. When an opioid binds to an opioid receptor, it causes a change in the electrical activity of the nerve cell. This change in electrical activity can lead to a decrease in pain perception.

The R-enantiomer of opioids has a higher affinity for the opioid receptors in the brain because it has a better fit for the receptor site. The S-enantiomer does not fit as well into the receptor site, so it is less potent.

In addition, the R-enantiomer of opioids is more resistant to metabolism than the S-enantiomer. This means that it stays in the body longer and can produce a longer-lasting effect.

The ability of the body to pick right opioid enantiomers is important for the effective use of opioid pain medication. By using the R-enantiomer, it is possible to achieve pain relief with a lower dose of medication, which can reduce the risk of side effects.