Plant-derived medicines for neuropathies: a comprehensive review of clinical evidence

Neuropathy is defined as the damage to the peripheral or central nervous system accompanied by pain, numbness, or muscle weakness, which can be due to congenital diseases or environmental factors such as diabetes, trauma, or viral infections. As current treatments are not sufficiently able to control the disease, studies focusing on the identification and discovery of new therapeutic agents are necessary. Natural products have been used for a long time for the management of different neurological problems including neuropathies. The aim of the present study is to review the current clinical data on the beneficial effects of medicinal plants in neuropathy. Electronic databases including PubMed, Scopus, and Cochrane Library were searched with the keywords 'neuropathy' in the title/abstract and 'plant' or 'extract' or 'herb' in the whole text from inception until August 2017. From a total of 3679 papers, 22 studies were finally included. Medicinal plants were evaluated clinically in several types of neuropathy, including diabetic neuropathy, chemotherapy-induced peripheral neuropathy, carpal tunnel syndrome, and HIV-associated neuropathy. Some studies reported the improvement in pain, nerve function, nerve conduction velocity, and quality of life. Cannabis sativa (hemp), Linum usitatissimum (linseed oil), capsaicin, and a polyherbal Japanese formulation called Goshajinkigan had the most evidence regarding their clinical efficacy. Other investigated herbal medicines in neuropathy, such as Matricaria chamomilla (chamomile), Curcuma longa (turmeric), and Citrullus colocynthis (colocynth), had only one clinical trial. Thus, future studies are necessary to confirm the safety and efficacy of such natural medicines as a complementary or alternative treatment for neuropathy.