Does having a Severe Mental Illness affect weight loss after bariatric surgery?
Research shows that people with severe mental illness (SMI) tend to lose slightly less weight after bariatric surgery compared to those without SMI. A 2023 meta-analysis found that mental illness was associated with a small but statistically significant reduction in weight loss 1. This may be partly because antipsychotic medications can disrupt glucose metabolism and promote weight gain, counteracting some surgical benefits 78. However, the effect is modest, and many people with SMI still achieve meaningful weight loss.
What the research says
A rapid review and meta-analysis of 23 studies (published 2001-2023) found that patients with preoperative mental illness had slightly lower weight loss after metabolic and bariatric surgery compared to those without mental illness (standardized mean difference -0.33, 95% CI -0.53 to -0.13) 1. This effect was similar in magnitude to that seen with type 2 diabetes or sleep apnea 1.
Antipsychotic medications, commonly used in SMI, are known to cause weight gain and dysregulated glucose homeostasis. A 2025 systematic review of 163 randomized trials found that antipsychotics can impair glucose control independently of weight gain, which may hinder postsurgical weight loss 7. Another review noted that diabetes prevalence is 2-3 times higher in people with SMI, and diabetes itself is linked to poorer surgical outcomes 8.
Despite these challenges, the absolute difference in weight loss is small. Many individuals with SMI still lose substantial weight after surgery. The key is to manage modifiable risk factors, such as medication choice and glucose control, in partnership with a healthcare team.
What to ask your doctor
- Could my antipsychotic medication affect my weight loss after bariatric surgery?
- Should I have my blood sugar checked before and after surgery?
- Are there medication adjustments that might improve my surgical outcomes?
- What lifestyle or behavioral support is available for people with mental illness after bariatric surgery?
- How much weight loss can I realistically expect given my health conditions?
This question is drawn from common patient questions about Psychiatry and answered using cited medical research. We do not provide individualized advice.