Chinese public health officials announced a blanket ban on all kinds of the powerful opioid fentanyl Monday, fulfilling a promise President Xi Jinping made to President Trump in December.

China already treats many types of fentanyl as controlled substances but only bans them one-by-one after time-consuming reviews. New variants are made before the old ones can be controlled. The regulation, which goes into effect May 1, will close loopholes that manufacturers in China have used before, including changing the fentanyl product just enough so it is no longer illegal.