B→Xsγ in supersymmetry: large contributions beyond the leading order

We discuss possible large contributions to B→Xsγ, which can occur at the next-to-leading order in supersymmetric models. They can originate from terms enhanced by tan β factors, when the ratio between the two Higgs vacuum expectation values is large, or by logarithm of MSUSY/MW, when the supersymmetric particles are considerably heavier than the W boson. We give compact formulae which include all potentially large higher-order contributions. We find that tan β terms at the next-to-leading order do not only appear from the Hall-Rattazzi-Sarid effect (the modified relation between the bottom mass and Yukawa coupling), but also from an analogous effect in the top-quark Yukawa coupling. Finally, we show how next-to-leading order corrections, in the large tan β region, can significantly reduce the limit on the charged-Higgs mass, even if supersymmetric particles are very heavy.