Local anesthesia is the injection of a solution that numbs the area where a dentist has to work on (tooth, gums, etc.) That solution can either contain epinephrine (adrenaline) or not. Epinephrine is added to the anesthesia solution to increase the numbing effect.

Anesthesia that contains epinephrine is commonly used, and the numbing effect lasts from 2 to 4 hours. Rarely does it last more than that, although there have been cases where the numbing effect lasted for days.

Anesthesia that doesn’t contain epinephrine is used for patients who have heart disease, high blood pressure, or patients who are allergic to epinephrine. The numbing effect is therefore shorter and can last around an hour.