How does local anesthesia work?

Stuart A. Linder, MD
Plastic Surgery

Local anesthetics work by specifically reducing pain in a local area that has been injected. Local anesthetics come in 2 forms, esters and amides. Those that end with caine, lidocaine, novocaine, and tetracaine, act similarly to cocaine. These can increase activity within the cardiac system. The amide anesthetics are the second group of anesthetics, usually of a longer half-life, up to 6 hours, such as bupivacaine or Marcaine.

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With local anesthesia, patients remain awake and conscious. Only a very small area of the body, such as a patch of skin, is made insensitive to pain. Typically, it provides both analgesia and paralysis by blocking nerve impulses so they can not travel to the brain. Still, patients may feel pressure and sensation.

Local anesthetics can be topical, where they are isolated just to the surface. These usually come in the form of gels, sprays or creams. They can be applied to the skin before an injection of local anesthetic that works to numb the area more deeply. The topical anesthetic is used to avoid the pain of the needle or even the drug itself (penicillin, for example, causes pain upon injection). Local anesthetics applied topically are not just used in medical procedures if you have ever used pain relief products for rashes or hemorrhoids, then you have used a topical anesthetic. An injected local anesthetic might be given before procedures including stitches or debridement (removing dead or damaged tissue).

Local anesthesia drugs usually end in the suffix "-aine" (such as novocaine, lidocaine or tetracaine). Actually, they"re chemically similar to cocaine which was the first local anesthetic. Two main problems with using cocaine as an anesthetic are that it is highly stimulating to the cardiovascular system and addictive. Synthetic alternatives were developed. These drugs can have negative side effects of their own, including allergic reactions. Therefore, these have fallen out of favor. Today, dentists typically use lidocaine rather than novocaine. Another issue with these drugs is that they are vasodilators they widen blood vessels. This could lead to excessive bleeding. Epinephrine can counteract this effect.

The local anesthesia usually wears off in about four to five hours. The pain relief, therefore, lasts longer than the medical procedure most of the time. There are typically very few side effects. Still, patients have to be careful with the numbed area. If you leave the dentist's office unable to feel part of your face, you might accidentally bite a cheek. In rare cases, nerve damage may result from injected local anesthetics, but they are typically low-risk when administered correctly to a healthy person.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.