Difelikefalin

How it works

Switches on kappa opioid receptors, not morphine's mu, and is built to stay out of the brain. Treats itch in people on dialysis.

What it's made of

Designed from scratch: 4 amino acids in “mirror” form (D), which enzymes barely recognize, joined to an artificial piece with a ring. It activates the kappa opioid receptor, not the mu receptor of morphine.

What it's for

Prescribed for

Moderate or severe itching from chronic kidney disease in adults on hemodialysis.