If you have schizophrenia, you are far more likely than your neighbour to develop type 2 diabetes. The relationship is now well established. A meta-analysis published in JAMA Psychiatry in 2017 by Vancampfort and colleagues found a pooled prevalence of diabetes in people with schizophrenia of roughly 11%, compared with around 5% in matched controls (Vancampfort et al., 2017). The difference is not subtle, and it is one of the largest contributors to the 13- to 15-year reduction in life expectancy seen in this population (Hjorthøj et al., 2017, Lancet Psychiatry).
Diabetes is two to three times more common in schizophrenia than in the general population, contributes substantially to early mortality, and remains badly under-screened — but it is detectable, treatable, and worth pushing for.
Why the risk is higher
The diabetes risk in schizophrenia is multifactorial. Three drivers combine:
Antipsychotic medication
Several second-generation antipsychotics — particularly olanzapine, clozapine, and quetiapine — increase weight, raise insulin resistance, and worsen glucose tolerance. The effect is not uniform: aripiprazole, lurasidone, and ziprasidone tend to be more weight-neutral. The FDA labels for olanzapine and clozapine carry warnings about hyperglycemia and diabetes risk (FDA Zyprexa label).
Illness-related risk that exists independent of medication
Studies of antipsychotic-naive first-episode patients have found higher fasting glucose and insulin resistance than in matched controls before any medication is given (Pillinger et al., 2017). This suggests a shared biological vulnerability — possibly involving inflammation, the HPA axis, and dysregulated glucose handling — that pre-dates treatment.
Lifestyle and care-system factors
Higher rates of smoking, lower rates of physical activity, food environments shaped by poverty and supportive housing, and limited access to primary care all compound the biological risk. Cognitive symptoms can make self-management — checking glucose, taking metformin daily, attending appointments — substantially harder.
What screening should look like
The American Diabetes Association and American Psychiatric Association published a joint consensus in 2004 (still widely used) recommending baseline and ongoing metabolic monitoring for everyone on a second-generation antipsychotic (Consensus Statement, Diabetes Care, 2004):
- Baseline: personal and family history, weight/BMI, waist circumference, blood pressure, fasting plasma glucose, fasting lipid profile.
- Weeks 4, 8, 12: weight.
- Quarterly: weight.
- Annually: fasting glucose (or HbA1c), lipids, blood pressure.
- Every 5 years: repeat fasting lipids if normal.
Adherence to these guidelines in real-world practice is poor. Multiple audits in the US and UK have found that fewer than half of patients on antipsychotics receive guideline-concordant glucose monitoring within the first year of treatment.
How diabetes is diagnosed
Diagnosis follows standard criteria — HbA1c ≥ 6.5%, fasting glucose ≥ 126 mg/dL, or a 2-hour oral glucose tolerance test result ≥ 200 mg/dL, on two occasions or with classic symptoms (ADA Standards of Care, 2024). Pre-diabetes is HbA1c 5.7–6.4% or fasting glucose 100–125 mg/dL — a range that should already trigger action, especially in this population.
What treatment looks like
Lifestyle
Modest weight loss (5–10% of body weight), increased activity, and improved diet have substantial effects on glucose control. Tailored programs for people with serious mental illness — such as the STRIDE and ACHIEVE trials — show real benefit when delivered with appropriate intensity and support (Daumit et al., 2013, NEJM). See our exercise and antipsychotic weight gain guide.
Metformin
Metformin is first-line oral therapy for type 2 diabetes and has independently been shown to mitigate antipsychotic-associated weight gain (our metformin article). It is generally well tolerated; the most common side effects are gastrointestinal.
GLP-1 receptor agonists
Drugs like semaglutide and liraglutide are increasingly used in patients on antipsychotics, with growing evidence of benefit for both glucose control and weight. Discussion with both the psychiatrist and primary-care doctor is important.
Insulin
Used when other agents are insufficient. Injection routines can be challenging for some patients with cognitive symptoms; long-acting basal insulins simplify the schedule.
Switching the antipsychotic
If diabetes develops on a high-risk agent (olanzapine, clozapine), switching to a more weight-neutral antipsychotic — when clinically possible — is a reasonable conversation. Clozapine is rarely switched away from when it is the only effective agent for treatment-resistant illness; in those cases, aggressive metabolic management alongside continued clozapine is the strategy.
Self-management when cognitive symptoms make it hard
- Use a pill organiser or a smartphone reminder app for metformin and any other oral agents.
- Connect a continuous glucose monitor (CGM) to a smartphone app — many models now do this; it removes the need to remember finger-stick checks.
- Build appointments into the same visit as your psychiatry follow-up where possible.
- Ask for diabetes educator referral; they specialise in teaching self-management at the patient's pace.
You have unexplained weight loss with extreme thirst, frequent urination, blurred vision, fruity-smelling breath, nausea, or confusion — these can be signs of diabetic ketoacidosis or severe hyperglycemia and require urgent evaluation.
Why this matters for life expectancy
Cardiovascular disease — driven heavily by diabetes — is the leading cause of premature death in schizophrenia. The Hjorthøj Lancet Psychiatry meta-analysis estimated that natural causes (mainly cardiometabolic disease) account for the majority of the life-expectancy gap. Catching diabetes early, treating it aggressively, and pairing it with smoking cessation, blood-pressure control, and statin use when indicated is one of the highest-impact things a care team can do.
Practical questions to ask your prescriber
- What was my last HbA1c, and when?
- Is my current antipsychotic among the higher-risk agents for diabetes?
- Should I be on metformin even if my HbA1c is in the pre-diabetes range?
- Can my psychiatrist coordinate with my primary-care doctor on monitoring?
The big picture
Diabetes in schizophrenia is common, predictable, and largely manageable — but it is also one of the most consistently neglected aspects of care. Pushing for monitoring, asking direct questions, and treating early changes the trajectory of the entire condition. It is one of the highest-leverage things a patient, family, or care team can do.
This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a qualified mental health professional. If you or someone you know is in crisis, call or text 988 in the US, or your local emergency number.