What is the clinical effectiveness of over-the-counter capsaicin products for the treatment of acute and chronic non-cancer pain?
What is the safety of over-the-counter capsaicin products for the treatment of acute and chronic non-cancer pain?
What is the cost-effectiveness of over-the-counter capsaicin products for the treatment of acute and chronic non-cancer pain?
The eight relevant publications identified comprised two systematic reviews with network meta-analysis (NMA), four randomized controlled trials (RCTs) and two economic evaluations. Six publications reported on clinical efficacy (related to pain relief) of capsaicin compared to other drugs. Four publications reported on neuropathic pain (peripheral neuropathic pain [PNP] or painful diabetic neuropathy [DPN]); these comprised one systematic review with network analysis (NMA) (with comparators: pregabalin, gabapentin, and duloxetine) and three non-inferiority randomized controlled trials (with comparators: pregabalin, amitriptyline, or clonidine; one each). For neuropathic pain, similar or non-inferior efficacy was reported for capsaicin (8%) patch compared to oral drugs (pregabalin, gabapentin, and duloxetine), and capsaicin (0.75%) cream compared to topical drugs (amitriptyline and clonidine). One systematic review with NMA involving patients with pain due to osteoarthritis, reported similar efficacy with capsaicin (0.0125% or 0.025%) compared to topical non-steroidal anti-inflammatory drugs. One randomized controlled trial involving patients with acute back and neck pain suggested greater efficacy with capsaicin (0.075%) compared with diclofenac, statistical significance was not reported. Four publications reported on safety outcomes (related to adverse events). These comprised one systematic review with NMA and three RCTs (two being non-inferiority trials). Capsaicin was associated with dermatological complications (application site pain, erythema, itching, and burning sensation) whereas pregabalin, gabapentin, and duloxetine were associated with somnolence, dizziness, and nausea. There was no statistically significant difference in headache events with capsaicin compared to pregabalin, gabapentin, or duloxetine. Itching was greater with capsaicin compared to amitriptyline or clonidine; statistical significance was not reported.One cost utility analysis showed that for patients with PNP, the probability of capsaicin (8%) patch being cost-effective versus optimized dose pregabalin was 97%, at a willingness to pay threshold of £20,000 per QALY. Another cost utility analysis showed that for patients with post-herpetic neuropathy (PHN), treatment with capsaicin (8%) patch versus oral agents (tricyclic antidepressant [TCA], gabapentin, pregabalin, or duloxetine) was cost-effective at a willingness to pay threshold of US$50,000 to US$100,000.Findings need to be interpreted with caution considering the limitations, such as limited quantity of evidence, variable quality of evidence, limited number of head-to-head trials comparing capsaicin with other agents, concerns related to reliability of findings from indirect comparisons, unclear long term effects, and potential biases; and for economic evaluations, findings are dependent on the assumptions on which the evaluations were based.