This randomized, double-blind, placebo-controlled, n-of-1 crossover study assessed whether metformin's side effects are reproducible in patients with a history of metformin intolerance. Participants completed up to four cycles of 2 weeks of metformin exposure and 2 weeks of placebo exposure. Participants completed surveys based on the Gastrointestinal Symptom Rating Scale and the Treatment Satisfaction Questionnaire for Medication. The primary hypotheses were that treatment satisfaction would be equal for placebo and metformin and that more than 30% of the study enrollees would be able to adhere to a higher dose of metformin 6 months after participation. Thirteen patients (all women, mean age 52.4 years) enrolled, three of whom were lost to follow-up or were non-adherent to study protocol. Metformin was associated with significantly lower global treatment satisfaction scores compared with placebo (39.58 vs. 53.75, P < .05 ) but participants could not distinguish metformin from placebo and did not report higher rates of gastrointestinal side effects on metformin. Two out of 10 participants adhered to a higher dose of metformin after trial completion. Metformin appears to have barriers to use beyond its classic gastrointestinal side effects.
Keywords: clinical trial; metformin; type 2 diabetes.
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