Weight is usually raised with rheumatoid arthritis patients as general health advice, alongside smoking and exercise, and it lands with about as much force. Today's data give it a different status.
In nearly 12,000 patients across 16 trials, response to JAK inhibitors fell stepwise as BMI rose, reaching a 22% relative reduction in ACR20 at class 3 obesity — and crucially, the same gradient did not appear in the placebo groups, so this is the drug working less well rather than heavier patients simply doing worse.
That converts weight from a lifestyle topic into a factor that changes how well the prescription will work, which is a different conversation and a more persuasive one. For a patient with class 2 or 3 obesity starting a JAK inhibitor, it is worth saying plainly that the drug is likely to work less well, that this is measurable rather than theoretical, and that weight management is therefore part of the arthritis treatment. It also argues for reviewing response earlier in these patients rather than assuming the usual timeline applies.
- Frame weight as affecting drug efficacy, not as general health advice
- Effect is measurable and stepwise, and absent under placebo
- Most consequential at class 2 and 3 obesity, minor at overweight
- Consider reviewing treatment response earlier in these patients
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