Metformin 用於預防抗精神病藥物引起之體重增加策略

Metformin for Prevention of Antipsychotic-Induced Weight Gain

8 out of 10 will experience antipsychotic-induced weight gain.

• Low and normal BMI individuals are at higher risk.
• Choice of antipsychotic is the most important predictor.
• Metformin is effective for preventing/treating weight gain.
• Lifestyle interventions should be offered to all patients.

Antipsychotic Risk Categories

• High Risk (first line): Olanzapine, Clozapine
• Medium Risk: Quetiapine, Paliperidone, Risperidone
• Lower Risk: All other antipsychotics

Metformin Initiation Criteria

• High Risk + comorbidity (HTN, DM, Pre-DM, PCOS, etc): Start Metformin
• Medium Risk + ≥3% weight gain at 4 weeks: Start Metformin
• Lower Risk or BMI ≥30 + comorbidity: Start Metformin or GLP-1 if unavailable

 

Avoid Metformin if:

• Acute metabolic acidosis
• Severe renal failure (GFR < 30)
• Hepatic insufficiency
• Alcohol abuse or harmful use

Pre-Treatment Monitoring

• Check renal function (GFR)

Dose Escalation Schedule

Week	Morning Dose	Evening Dose
1	500 mg	–
2	500 mg	500 mg
4	1 g	500 mg
6	1 g	1 g

Useful Notes

• Take with food to reduce GI side effects.
• Adjust max dose if GFR 30–44 mL/min: Max 1g/day.
• Slow-release metformin preferred in poor tolerance or adherence.
• Metformin is low cost.

Side Effects

• Common (≤1 in 10): GI upset, appetite loss, Vit B12 deficiency
• Uncommon (<1 in 100): Taste disturbance
• Rare (<1 in 1000): Lactic acidosis, skin/LFT issues

Ongoing Monitoring

• Weight, BMI
• Lactic acidosis symptoms
• Vitamin B12 in long-term therapy or elderly/malnourished

When to Stop

• At risk or with lactic acidosis
• Dehydration or surgery with fluid restriction
• Sepsis or renal impairment (GFR < 30)
• Temporarily for contrast studies (48h pause)

Reassess need periodically. If stopped for acute illness, restart once well.

Source: St. Vincent’s University Hospital / St. John of God / HRB / Progress