Objective The objective was to show the superiority of comfrey root extract ointment to placebo ointment in patients with acute upper or lower back pain.

Design The study was conducted as a double-blind, multicentre, randomised clinical trial with parallel group design over a period of 5 days (SD 1). The patients (n = 120, mean age 36.9 years) were treated with verum or placebo ointment three times a day, 4 g ointment per application. The trial included four visits.

Main Outcome Measures The primary efficacy variable was the area under the curve (AUC) of the visual analogue scale (VAS) on active standardised movement values at visits 1 to 4. The secondary efficacy variables were back pain at rest using assessment by the patient on VAS, pressure algometry (pain–time curve; AUC over 5 days), global assessment of efficacy by the patient and the investigator, consumption of analgesic medication and functional impairment measured using the Oswestry disability index.

Results There was a significant treatment difference between comfrey extract and placebo regarding the primary variable. In the course of the trial the pain intensity on active standardised movement decreased on average (median) approximately 95.2% in the verum group and 37.8% in the placebo group.

Conclusions The results of this clinical trial were clear-cut and consistent across all primary and secondary efficacy variables. Comfrey root extract showed a remarkably potent and clinically relevant effect in reducing acute back pain. For the first time a fast-acting effect of the ointment (1 h) was also witnessed.