Impact of Metformin-Induced Gastrointestinal Symptoms on Quality of Life and Adherence in Patients with Type 2 Diabetes

Aims: Gastrointestinal (GI) symptoms are common in patients with type 2 diabetes mellitus (T2DM). This study assesses the impact of 1) metformin on GI symptoms and health-related quality of life (HRQoL) and 2) metformin-associated GI symptoms on medication adherence in patients with type 2 diabetes newly beginning therapy. Methods: Patients with T2DM aged >= 18 years starting metformin from January to June 2007 who filled their prescriptions for >= 3 months were identified from a health benefits company database. Via telephone, GI symptom impact was evaluated in a 360-patient sample using the validated Bowel Symptom Questionnaire and Medical Outcomes Study 36-Item Short-Form Health (SF-36) survey. Adherence was assessed using the medication possession ratio (MPR). Logistic regression adjusting for demographic and clinical covariates was used to assess the relationship between GI symptoms and MPR < 80%. Results: The most and least common GI symptoms reported were diarrhea (62.1%) and retching (21.1%), respectively. Most GI symptoms were associated with lower physical and mental HRQoL (P < 0.05). Most changes in specific HRQoL reached the minimum important difference of 3 points. Bloating, nausea, and abdominal pain were significantly associated with MPR < 80%. Adjustment for demographic, clinical, and HRQoL factors made these relationships less evident. Conclusions: Metformin-associated GI symptoms in patients with T2DM lead to lower physical and mental HRQoL, which may result in patient nonadherence or physician reluctance to optimally titrate the metformin dose.