RESEARCH QUESTION / RATIONALE High rates of antipsychotic induced weight gain (AiWG) in patients treated with antipsychotics (50%) negatively impact health, treatment adherence and quality of life.
HYPOTHESIS: Metformin when given adjunctively to lifestyle interventions outperforms placebo and results in meaningful weight decreases and quality of life increases.
STUDY DESIGN: Randomized, double blind, placebo-controlled trial.
STUDY POPULATION: Patients who use antipsychotics for schizophrenia spectrum disorders, with BMI>25 and who are willing to do lifestyle interventions to reduce weight.
INTERVENTION AND COMPARATOR: The intervention is metformin and the comparator placebo.
OUTCOME PARAMETERS: the primary outcome measure is difference in weight (from treatment inception until 26 weeks of treatment). Secondary outcomes are 1) All other elements of metabolic syndrome 2) Quality of life 3) ) General psychological and physical health 4) Cost-effectiveness. Most relevant safety outcomes are adverse drug reactions.
DATA-ANALYSIS: The primary analysis in this trial tests the effect of metformin prescription on body weight with a primary comparison at 26 weeks after treatment onset. This will be analysed using a general linear mixed model with treatment group, baseline weight, gender and age as fixed factors and patient as random factors
SAMPLE SIZE CALCULATION: We have 80% power at a two-sided 0.05 significance level to detect a difference in weight reduction of 2 kgs (SD=4, ES=0.5) after 26 weeks in 128 participants.