Patients with acute lumbar disc prolapse with sciatica who are not considered candidates for surgery are usually treated with physiotherapy and non-steroidal anti-inflammatory agents. Moreover, the treatment with benzodiazepines is common practice in the absence of class I or II level of evidence. Here we assessed the role of benzodiazepines in the conservative management of acute lumbar disc prolapse. Using a placebo-controlled, double-blinded design, 60 patients were randomized to receive placebo or diazepam in addition to mechanical physiotherapy and analgesics for the first 7 days of conservative treatment of clinically and radiologically confirmed lumbar disc prolapse. The primary objective was to evaluate if physiotherapy plus analgesics, but without benzodiazepines, is equivalent to the same therapy plus benzodiazepines. The primary endpoint was centralization of referred pain at day 7. Twenty-six female and 34 male patients were enrolled. The median age was 42 years (range 22-68 years). Analysis of the primary endpoint demonstrated equivalence between placebo and diazepam (median 60% vs. 50% reduction of distance of referred pain at day 7) within the predefined equivalence tolerance of 20% at a significance level of p<0.05. Regarding the secondary endpoints, the median duration of the stay in hospital was shorter in the placebo arm (8 vs. 10 days, p=0.008), and the probability of pain reduction on a visual analog scale by more than 50% was twice as high in placebo patients (p<0.0015). Benzodiazepines should not be used routinely in patients treated with mechanical physiotherapy for lumbar disc prolapse.