"Abel smiles a lot when he's with this special person, and so his whole face goes a little numb. Abel isn't the first singer to compare the euphoria of love to that provided by drugs - just ask Ghostface.
While many drugs are associated with numbness, including novocaine and Ketamine, the classic face-numbing drug is cocaine. For years cocaine was used by doctors as a numbing agent and local anaesthetic. Although it's rarely used in healthcare anymore, the suffix "caine," which originally just meant "of the coca plant," is still used in pharmaceutical contexts to indicate a numbing compound, e.g. novocaine.
The personification of cocaine in the song climaxes in the hook. In recent singles, Abel has referenced his addiction to drugs - and the reason he can't stop is the numb-euphoric rush he gets from narcotics."