Do I need FDA registration to blend supplement powders?

Yes. Any facility that manufactures, packages, labels, or holds dietary supplements for sale in the US must register with the FDA under 21 CFR Part 1 and comply with GMP regulations in 21 CFR Part 111. If you outsource blending to a co-manufacturer, their facility registration covers the production — but you as the brand owner still hold responsibility for formula compliance and label accuracy.