trials found that for every two people treated with topical lidocaine, one person experienced at least a 50% reduction in their PHN-associated pain (number needed to treat (NNT)=2). Low-dose capsaicin may be useful for reducing PHN-associated pain but is limited by side effects (redness and a burning or stinging sensation with application) and the need to apply it four times daily. Approximately three people must be treated with low-dose capsaicin cream for one person to experience significant pain relief (number needed to treat =3.3). A single topical application of a high-dose capsaicin patch over the affected area after numbing the area with a topical anesthetic has also been found to relieve PHN-associated pain. For every eleven people treated with a high-dose capsaicin patch for up to 12 weeks, one person experienced a significant improvement in their pain. (number needed to treat=11). Due to the need for topical anesthesia before application of the high-dose capsaicin patch, referral to a pain specialist is generally recommended if this approach is being considered. Oral medications Multiple oral medications have demonstrated efficacy in relieving postherpetic neuralgia pain. Tricyclic antidepressants (TCAs), such as nortriptyline or desipramine, are effective in reducing postherpetic neuralgia pain but are limited by their numerous side effects. For every three people treated with a tricyclic antidepressant, one person is expected to have a clinically significant reduction in their pain (NNT=3). Additionally, of every sixteen people treated with a TCA, one person is expected to stop the medication due to a bothersome side effect, such as dry mouth, constipation, or urinary retention (number needed to harm=16). The anticonvulsant medications pregabalin and gabapentin also effectively relieve postherpetic neuralgia pain. Treatment with pregabalin leads to a reduction in pain intensity of 50% or more in one person out of every 4–5 people treated (NNT=4–5). Similarly, treatment with gabapentin also leads to a 50% reduction in pain intensity in one person out of every 7-8 people treated (NNT=7.5). Opioids such as tramadol, methadone, oxycodone, and morphine have not been well-studied for postherpetic neuralgia treatment. Acetaminophen and nonsteroidal anti-inflammatory drugs are thought to be ineffective and have not undergone rigorous study for PHN. Prognosis The natural history of postherpetic neuralgia involves slow resolution of the pain syndrome. A subgroup of affected individuals may develop severe, long-lasting pain that does not respond to medical therapy. References Further reading External links Virus-related cutaneous conditions Neurological disorders Pain Varicella zoster