The placebo effect in early-phase glaucoma clinical trials.

Purpose: To analyze the extent and prevalence of the placebo effect in prior early-phase glaucoma clinical studies.

Methods: Articles were evaluated on phase I and II trials of glaucoma medicines that became commercially available after 1977 with a placebo arm that involved glaucoma patients.

Results: We included 23 studies with 23 treatment arms with a total of 1703 patients in articles evaluating 10 different glaucoma medications. This study showed that at 8 AM (n = 18), the average decrease in placebo from untreated baseline was 2.3 ± 1.6 mm Hg (9%), while for the diurnal curve (n = 17), the mean decrease was 1.4 ± 1.1 mm Hg (6%). At 8 AM, 8/18 treatment arms had greater than 2 mm Hg intraocular pressure (IOP) decrease, and all had at least some reduction in IOP. For the diurnal curve, 4 of 17 studies had reduced IOP greater than 2 mm Hg. One treatment arm had no placebo effect.

Conclusions: This study suggests that a placebo effect is common in glaucoma clinical trials and potentially could limit the ability to evaluate the efficacy of a new medicine.