Weight is recorded in most rheumatology clinics and used in almost none of them, beyond a comorbidity list. Today's JAK inhibitor data give it a direct role in the drug decision: the expected benefit is measurably smaller as BMI rises, and the effect is specific to the drug rather than to the disease.
The practical move costs nothing. Weigh at the visit where treatment is chosen, not at the follow-up, and say the number out loud as part of the discussion about what the drug is expected to do. A patient told at the start that weight will affect how well the treatment works is a different conversation from one told it six months later when the drug has underperformed.
It also changes what a non-response means. Before switching class for inadequate response, it is worth asking whether weight was ever part of the plan. Switching to a second JAK inhibitor in a patient with class 3 obesity, having never addressed the modifier, repeats the experiment.
- Weigh at the decision visit, not only at review.
- State the expected effect of BMI on response while choosing the drug.
- Before switching for non-response, check whether weight was ever addressed.
- Arrange the weight-management route at the same appointment, with a name attached.
The statistics, in plain English
This pearl rests on the JAK inhibitor meta-analysis above rather than on a separate study, and it inherits that evidence: an observed gradient of response across BMI bands, absent in the placebo arms. It is an association from trial data, not a demonstration that losing weight improves response — no trial has randomised patients to weight loss and measured JAK inhibitor efficacy afterwards. Treat it as a reason to raise weight early, not as a promise that addressing it will restore the response.
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