Telehealth companies including Hims & Hers, Sesame and Noom have flocked to Facebook and Instagram to promote their booming weight loss drugs.

But pressure from regulators concerned about consumers' health data privacy has prompted Meta Platforms to limit how advertisers target users with health-related ads, starting this month. That is upending weight loss campaigns in the middle of the New Year's resolution marketing season. And more broadly, marketers are scrambling to figure out exactly what kind of weight loss and other health-related products are affected, and trying out workarounds for the new rules.