After a person injects, eats, smokes, or snorts a drug, drug molecules enter the bloodstream and eventually make their way to the brain where they bind to particular receptors on the surface of neurons. A drug vaccine would stop that process—the immune system would attack those molecules while they’re still in the blood. But the immune system doesn’t naturally assume that the molecules are invaders that need to be attacked, so it needs to be trained.

“You have to trick the body, and it requires a fair amount of trickery,” Skolnick says. In practice, that means binding molecules with a similar structure to those of the drug in question with antigens, molecules that trigger an immune response. Over time, the immune system would learn to attack drug molecules. Most vaccines so far have targeted a single compound, but it could be possible to have a polyvalent vaccine that can address several at once.

Scientists were able to demonstrate a working vaccine recently in mice.