Weight Gain and Blood Sugar Levels in Antipsychotic Treatment

Rapid Metabolic Shifts in the First Ninety Days

Weight gain and blood sugar levels in antipsychotic treatment accelerate most rapidly during the first three months of therapy. Researchers from Karolinska Institutet and University College London evaluated electronic health records from nearly 97,000 patients in England aged 18 to 59 with severe mental illness. The study tracked changes before and after patients started second-generation antipsychotic medication.

During the first 90 days, weight rose by an average of 0.21 kilograms (0.46 pounds) per week. That compares to an increase of 0.02 kilograms (0.04 pounds) per week before treatment began. Over the same 90-day window, hemoglobin A1c (HbA1c) climbed by an average of 0.12 mmol/mol each week, compared to 0.01 mmol/mol weekly prior to starting the medication.

The pace of change dropped substantially after three months. From day 91 through two years, weight gain slowed to 0.03 kilograms (0.07 pounds) per week. Weekly HbA1c increases dropped back to 0.01 mmol/mol across that extended follow-up window.

Different Outcomes by Medication and Baseline Risk

Metabolic changes varied by the specific medication prescribed to each patient. Olanzapine caused the largest increases in both weight and blood sugar measurements. Quetiapine led to notable weight gains as well, but it produced only small shifts in HbA1c.

Patient characteristics influenced the extent of metabolic changes during therapy. Women showed larger increases in weight and blood sugar than men. Existing metabolic status at the start of treatment also had a significant effect on long-term outcomes.

Patients with prediabetes when therapy began faced a much higher likelihood of progressing to type 2 diabetes. Within two years, an estimated 19% of patients with prediabetes developed diabetes. Among individuals who began medication with normal HbA1c levels, 3% developed diabetes over the same period.

Study Structure and Health Record Limitations

The findings come from an observational interrupted time-series analysis rather than a randomized clinical trial. The authors extracted routine primary care records to examine real-world clinical patterns across England. This observational structure means the analysis identifies associations rather than direct experimental proofs.

Missing routine laboratory measurements represent another key constraint in the dataset. While just over three-quarters of the 97,000 patients had at least one recorded weight check, only about one-quarter had at least one recorded HbA1c measurement. Gaps in clinical testing reduce the precision of the overall blood glucose estimates.

Early Monitoring for Weight and Blood Sugar Levels

The concentration of metabolic changes in the early weeks points to a clear window for clinical tracking. Study co-author Magnus Boman noted that the greatest shifts occur early, indicating that clinicians should track weight and blood sugar from day one through the first three months.

Patients starting antipsychotic therapy should discuss baseline metabolic screening and a ninety-day monitoring plan with their prescribing clinician.