The preparation of an acceptable placebo for NPH insulin.

A suitable placebo for NPH insulin has not previously been available for clinical investigation. A series of organic and inorganic compounds were formulated as insulin placebos and analyzed according to the following criteria: (1) degree of visual similarity to insulin, (2) stability, (3) absence of local side effects, and (4) clinical safety. Dilute suspensions of cortisone acetate (1.25-2.5 mg/ml) were found to fulfill the criteria as acceptable insulin placebos. Placebo-controlled studies with NPH insulin can now be performed.