Hydroxyzine is an antihistamine drug used for symptomatic relief of anxiety and tension. We hypothesized that managing the anxiety of patients with severe pain by adding hydroxyzine to a conventional intravenous morphine titration would relieve their pain more effectively.

This was a randomized, double-blind, controlled group study of prehospital patients with acute pain scored greater than or equal to 6 on a 0–10 verbal numeric rating scale (NRS). Patients'anxiety was measured with the self-reported Face Anxiety Scale (FAS) ranking from 0 to 4. The percentage of patients with pain relief (NRS score ≤ 3) 15 min after the first injection was the primary outcome.

One hundred forty patients were enrolled. Fifty-one percent (95% CI 39% to 63%) of hydroxyzine patients versus 52% (95% CI 40% to 64%) of placebo patients reported a pain numeric rating scale score of 3 or lower at 15 min. Ninety-one percent (95% CI 83% to 98%) of patients receiving hydroxyzine reported no more severe anxiety versus 78% (95% CI 68% to 88%) of patients with placebo (p > 0.05). Adverse events were minor, with no difference between groups (6% in hydroxyzine patients and 14% in placebo patients).

Addition of hydroxyzine to morphine in the prehospital setting did not reduce pain or anxiety in patients with acute severe pain and therefore is not indicated based on our results.