Topically applied capsaicin (CAS 404-86-4) induces the release of substance P, a neurotransmitter, from sensory C-fibres. In addition, there is a specific blockade of transport and de-novo synthesis of substance P. As a result, repeated applications of capsaicin bring about a long lasting desensitisation to pain (increase of pain threshold). The desensitising effect is fully reversible. The confirmed pharmacodynamic actions and a number of double-blind clinical studies indicate that local capsicum preparations are very suitable for the treatment of neuropathic pain or musculoskeletal disorders, with or without inflammatory components. In a double-blind, randomised parallel-group study a capsicum plaster was compared with a placebo for 3 weeks in 154 patients with non-specific back pain. Inclusion criteria were a history of back pain for a minimum period of 3 months and a degree of pain of 5 or more on an eleven grade visual analogue scale. The principal target variable consisted of the score of 3 combined pain scales. Secondary efficacy measures were tests of mobility, a disability index (in the context of Arhus low back rating scale) and global assessments by physicians and patients. For patients to be rated as responders their total pain score at the final examination after 3 weeks of treatment had to show a reduction by at least 30% of the baseline value. The study unequivocally achieved the target criterion with a rate of responders in the capsicum group of 60.8% against 42.1% in the placebo group (p = 0.0219). The sum of the 3 separate pain scales decreased more markedly in the capsicum group than in the placebo group (38.5% compared to 28.0%; p = 0.002). Relatively slight improvements of the impaired mobility and the functional status are explained by the characteristics of the disorder treated. The efficacy ratings by observers and patients was definitely in favour of capsicum. Adverse effects--mostly harmless and resolving spontaneously--were reported by 15 patients in the capsicum group and by 9 in the placebo group. The tolerance ratings by investigators and patients were superior to the placebo product. This, however, partly is due to the local pharmacological actions of the drug. As in comparably positive randomised studies with capsaicin cream in patients with osteoarthritis or fibromyalgia it was shown that a capsicum plaster preparation can also be used to advantage in chronic non-specific back pain.