Local anesthetics are generally safe and usually don’t cause any side effects, aside from some tingling as it wears off. However, if you’re given too much, or the injection goes into a vein instead of tissue, you might have more side effects, such as: ringing in your ears dizziness numbness twitching a metallic taste in your mouth In extremely rare cases involving very high doses, anesthesia may cause: seizures low blood pressure slowed heart rate breathing problems