The effects of lidocaine usually last for about 20 minutes, according to MedicineNet. Lidocaine is injected to numb an area before a procedure.
The Food and Drug administration approved the use of lidocaine as an anesthetic in 1949, states MedicineNet. This drug is used to numb a certain area of the body without affecting the surrounding nerves. The medicine will begin numbing the area within 90 seconds. It hinders nerve impulses from reaching the brain so the patient does not feel pain. Some side effects include pain at the injection site, dizziness, weakness and drowsiness. Lidocaine is safe for pregnant women as there are no known side effects to the fetus.