A 38-year-old man with schizophrenia has been on risperidone 6 mg/day for 2 years. He presents with progressive weight gain (12 kg over 18 months), fasting blood glucose 128 mg/dL, and triglycerides 220 mg/dL. Which is the most common metabolic side effect associated with atypical antipsychotics?

Explanation

## Metabolic Side Effects of Atypical Antipsychotics **High-Yield:** Weight gain is the most frequent and earliest-appearing metabolic adverse effect of atypical antipsychotics, occurring in 40–60% of patients within the first 3–6 months of treatment. ### Frequency and Timeline **Key Point:** Weight gain typically precedes and may predict the development of other metabolic complications (dyslipidemia, hyperglycemia, metabolic syndrome). | Metabolic Complication | Frequency | Onset | Mechanism | |---|---|---|---| | **Weight gain** | 40–60% | 3–6 weeks | H1-receptor blockade, 5-HT2C antagonism, appetite ↑ | | **Dyslipidemia** | 20–40% | 3–6 months | Insulin resistance, weight gain | | **Hyperglycemia** | 10–20% | 3–12 months | Direct β-cell dysfunction, insulin resistance | | **Hypertension** | 5–15% | Variable | Weight gain, metabolic syndrome | ### Risk Stratification by Agent **Mnemonic:** **CLAP** — Clozapine, Olanzapine, Aripiprazole (partial), Paliperidone (moderate) — ranked by metabolic risk. - **Highest risk:** Clozapine, olanzapine (>5 kg average gain) - **Moderate risk:** Risperidone, paliperidone (2–3 kg average gain) - **Lower risk:** Aripiprazole, ziprasidone, amisulpride ### Clinical Pearl **Warning:** Weight gain is often the earliest sign of metabolic dysfunction and a major cause of non-adherence. Baseline weight, BMI, waist circumference, fasting glucose, and lipid panel should be documented before starting therapy and monitored at 4, 8, and 12 weeks, then annually [cite:Maudsley Guidelines 2023]. ### Pathophysiology 1. **H1-receptor antagonism** → increased appetite and sedation 2. **5-HT2C receptor blockade** → loss of satiety signalling 3. **Insulin resistance** (independent of weight gain in some agents) 4. **Leptin dysregulation** → impaired appetite suppression **Clinical Pearl:** The temporal sequence is typically: weight gain → dyslipidemia → hyperglycemia → metabolic syndrome. Intervention at the weight gain stage can prevent progression.