Factors associated with the prophylactic effect of placebo injections in subjects enrolled in a study of botulinum toxin for migraine

We set out to identify predictors for the prophylactic effect of placebo injections in subjects with migraine by post hoc analysis of 81 subjects with episodic migraine receiving single-blind placebo injections in a prospective trial of botulinum toxin. Possible predictors of placebo prophylaxis were compared among placebo responders (PRs) and placebo non-responders (PNRs). There were 34 PRs (42%) and 47 PNRs (58%). Male gender [odds ratio (OR) 5.83, 95% confidence interval (CI) 1.12, 30.14, P = 0.022], a history of opioid use (OR 4.44, 95% CI 1.47, 13.41, P = 0.005) and injections in the neck/shoulders (OR 2.44, 95% CI 0.93, 3.19, P = 0.033) were associated with placebo response. Of subjects with two or more of these signs, 88% were PRs compared with 31% of subjects with one or less. Male gender, opioid use and injections in the neck/shoulders are associated with placebo prophylaxis. These findings may have important implications for the design of future clinical trials and for the clinical management of migraineurs.