Objective The aim of this study was to determine the effect of intra-muscular benztropine on pain and range of motion in patients presenting to the emergency department with acute, non-traumatic neck pain (wry neck).

Methods In this two-centre randomised, double-blind, placebo-controlled, parallel-group superiority trial, participants were allocated to receive 2 mg intramuscular benztropine or normal saline. Participants were aged 16–65 years, no history of neck disorders and no use of medication that cause dystonia. Randomisation was computer generated, with allocation concealment by opaque sequentially numbered sealed envelopes. Pain scores and neck range of motion were measured immediately before drug administration, and 30 min after. Pain scores, range of motion and adverse effects were compared between the groups. No funding was received. The trial was registered.

Results Thirty participants were enrolled, 15 randomised to placebo and 15 to benztropine. Pain scores at 30 min were lower in those allocated to benztropine, but the difference was neither statistically nor clinically significant (0.6 points, 95% CI −0.8 to 1.8, p=0.40). The range of motion of the cervical spine was greater in those receiving benztropine, but the differences were very small and not statistically significant. Adverse events were more common in those receiving benztropine.

Conclusions Benztropine was ineffective for reducing pain or improving range of motion of the cervical spine in patients suffering from acute, non-traumatic neck pain, but frequently caused anticholinergic side effects. However, as the CI for the primary outcome included the minimum difference considered clinically significant, an important effect of benztropine cannot be ruled out.

Trial registration number ANZCTR#12612000354886