Table 1 Inclusion criteria for considering studies for this review

Types of studies

Randomized controlled trials (RTCs), quasi-randomized controlled trials, and controlled clinical trials (CCTs) with no language restriction.

Types of participants

Adults suffering from pain in the musculoskeletal system due to osteoarthritis or low back pain.

Types of interventions

Studies utilizing preparations of Harpagophytum procumbens were included. Preparations may differ in the solvent (water, alcohol) used to prepare the extract (if not crude powdered plant material is used), the drug extract ratio, and the galenic aplication form. They also differ in the content of the active principles (the sum of active ingredients) and in the quantity of the co-active marker compound harpagoside (Chrubasik et al. 1996, Sporer and Chrubasik 1999).

Types of outcome measures

Primary outcome: pain (e.g. visual analogue scale, visual rating scale, pain component of the disease-specific Arhus Low Back Pain Index, component pain of the Western Ontario MacMaster (WOMAC) instrument). Secondary outcomes: number of pain-free patients (defined as being pain-free on at least five days in the last treatment week without taking any rescue medication see above), functional indices (e.g. Lequesne index, finger-ground distance), and generic outcome measures [global assessments, health assessment questionnaire (HAQ)] or the consumption of additional analgesic treatment.