The Primary Numbing Sensation
Lidocaine’s primary and intended effect is to produce a localized numbness or loss of feeling. This is achieved by blocking voltage-gated sodium channels in the nerve cell membranes, which prevents the initiation and transmission of pain signals to the brain. For most patients, this process is smooth, replacing painful stimuli with a profound sensation of numbness. The exact feeling can vary significantly based on how the medication is administered.
How The Numbing Varies by Application Method
The sensation of numbing differs based on the form and route of administration. Here is a breakdown of what to expect from common lidocaine applications:
- Lidocaine Injection: In dental procedures or minor surgery, a localized injection leads to a complete loss of sensation and sometimes temporary muscle function in the target area. For instance, a dental injection can numb the mouth, tongue, and cheeks, making it crucial to avoid chewing until the feeling returns. In epidurals, it can cause a temporary loss of sensation and movement in the lower half of the body.
- Topical Creams and Patches: Applied directly to the skin, these forms offer a less profound numbing effect. Initial sensations may include tingling, warmth, or a mild burning where the product is applied. The skin may also appear blanched or red before becoming numb. This provides targeted relief for conditions like shingles or minor burns.
- Viscous Solution (Oral): When used for mouth or throat sores, the solution creates a numbing effect that can impact the ability to swallow and can feel strange. Patients are advised to be cautious when eating or drinking to prevent accidentally biting their tongue or cheeks.
- Intravenous (IV) Infusion: Used to treat neuropathic pain or certain cardiac conditions, an IV infusion delivers lidocaine systemically. This can produce more widespread effects, including a metallic taste, tingling around the mouth, or a general feeling of warmth.
When the Numbing Wears Off
As the body metabolizes lidocaine, the numbing effect gradually diminishes and sensation returns. This process typically begins with a tingling, or “pins-and-needles” sensation, similar to how a limb feels when it “wakes up”. This is a normal part of the process and can be followed by a gradual return of touch, temperature, and pressure sensitivity. In procedures with tissue trauma, such as surgery or dental work, a mild level of pain or discomfort may emerge as the anesthesia wears off. Your healthcare provider may recommend an over-the-counter pain reliever to manage this period.
Common Side Effects and Adverse Reactions
While local applications of lidocaine are generally safe, higher doses or accidental systemic absorption can cause a range of side effects. Common side effects may include:
- Dizziness or lightheadedness
- Drowsiness
- Anxiety or nervousness
- Mild nausea or vomiting
Central Nervous System (CNS) Effects at Higher Doses
When lidocaine levels in the bloodstream are too high, the drug can affect the central nervous system, leading to more pronounced symptoms. The sequence of CNS toxicity is often progressive, but can vary by individual. Early signs can include restlessness, euphoria, blurred vision, ringing in the ears (tinnitus), and a metallic taste. As toxicity increases, symptoms can progress to muscle twitching, tremors, and seizures. Psychological reactions have also been reported, including anxiety, confusion, and even a profound “doom anxiety” at toxic levels. These symptoms usually resolve quickly once the infusion is stopped.
Rare but Serious Concerns
Two rare but serious adverse reactions are methemoglobinemia and severe allergic reactions. Methemoglobinemia is a blood disorder that can cause symptoms like pale, blue, or gray skin, headache, confusion, and shortness of breath. Allergic reactions are characterized by symptoms such as rash, itching, hives, and swelling of the face, lips, or tongue. If you experience any of these serious symptoms, seek immediate medical attention.
Lidocaine Formulations and Their Effects: A Comparison
| Feature | Topical Cream/Patch | Local Injection (Dental/Surgical) | IV Infusion (Neuropathic Pain) |
|---|---|---|---|
| Sensation | Tingling, warmth, and targeted skin numbing. | Targeted, profound loss of sensation and motor function. | Systemic effects: metallic taste, tingling around mouth, general numbing. |
| Onset | 30–60 minutes for creams; often longer for patches. | Almost immediate; within minutes. | Continuous, gradual effect based on infusion rate. |
| Duration | Up to several hours. | 1–3 hours for lidocaine alone; longer with epinephrine. | Maintained throughout the infusion. |
| Common Side Effects | Local irritation, redness, skin blisters. | Local pain or redness at injection site. | Dizziness, drowsiness, nausea. |
| Risk of Systemic Effects | Low, if used as directed. Increased with overuse or damaged skin. | Very low, managed by healthcare professionals. | Higher, as it is delivered systemically. |
The Difference Between Systemic and Local Effects
It is crucial to differentiate between the local, targeted numbing effect and the systemic effects that can arise from higher concentrations in the bloodstream. For a dental injection, the goal is to keep the anesthetic localized to block a specific nerve bundle. However, with an intravenous infusion, the medication is delivered into the entire bloodstream to reduce widespread nerve pain. When higher-than-recommended doses are used topically, or if an injection is administered incorrectly, a higher-than-intended amount can be absorbed systemically, potentially causing adverse effects.
Conclusion
For most people receiving a standard dose from a qualified practitioner, the feeling of lidocaine is a targeted, reassuring numbness that makes a medical procedure manageable. As the numbing wears off, a pins-and-needles sensation is normal, followed by a gradual return of feeling. Side effects like dizziness, drowsiness, or anxiety are usually mild and related to higher systemic doses, but it is important to be aware of them. Anyone experiencing severe or unusual symptoms should contact a healthcare professional immediately. The experience of using lidocaine is highly dependent on the dose and administration method, so always follow your doctor's instructions to ensure a safe and comfortable experience.
For more information on the various applications and safety precautions, consider consulting the Lidocaine page on the Mayo Clinic website.
