Design: Individual patient data meta-analysis of 16 phase 3 RCTs
Population: 11,883 adults with rheumatoid arthritis
Primary outcome: ACR20 response and DAS28-CRP at primary endpoint
Effect: ACR20 RR 0.94 (overweight) to 0.78 (0.71 to 0.85) in class 3 obesity

This individual patient data meta-analysis used 16 phase 3 trials of tofacitinib, baricitinib and upadacitinib (11,883 patients with RA). Median BMI was 26.8, and 31% had obesity. Risk of bias was low.

Compared with healthy weight, the relative risk of ACR20 response was 0.94 with overweight, 0.92 with class 1 obesity, 0.88 with class 2 and 0.78 with class 3 (0.71 to 0.85). DAS28-CRP was correspondingly worse, by 0.54 points in class 3 obesity. There was no BMI gradient on placebo, so obesity reduced the drug's effect rather than simply marking worse disease.

For patients with severe obesity, expected response to a JAK inhibitor is meaningfully lower. Weight management is part of RA treatment, not an add-on.

Discuss the lower expected response when starting a JAK inhibitor in patients with obesity.
Offer structured weight management alongside advanced therapy.
Weigh JAK inhibitor cardiovascular and VTE risks, which are also higher with obesity.
Reassess response at 12 weeks and switch early if inadequate.

Why it matters

It shows obesity changes how well a drug works, not just how sick the patient is.

The statistics, in plain English

A relative risk of 0.78 means patients with class 3 obesity were 22% less likely to reach ACR20 than those of healthy weight. The absence of a gradient on placebo is what shows this is an interaction with the drug. Low heterogeneity (I² up to 40%) means trials agreed.