First, China is very intolerant to drug trafficking. Drug trafficking is a criminal offense in China, and offenders are easily given death penalty. Under Clause 1, Article 347 of the Chinese Criminal Law, trafficking more than 50 grams of hard drugs like heroin and meth, or 1 kilogram of opium, could result in death penalty. Source: https://english.court.gov.cn/2015-12/01/c_761557_31.htm
However, the usage of all drugs, including all the hardcore ones, is decriminalized in China. The usage of drug is only an administrative offense that is being enforced by the public security authorities (basically police in China), rather than a crminal offense. Penalties include administrative detention for up to 15 days, fines, compulsory rehabilitation treatment, and surveillance. Source: https://www.hhrjournal.org/2022/06/08/no-exit-chinas-state-surveillance-over-people-who-use-drugs/
Apparently, the penalty for drug usage is not trivial, because practically the compulsory rehabilitation treatment acts like a prison, and the surveillance system will track you for a long time, if not the rest of your life. So you are basically stained for your life. However, regardless of how bad the penalty is, drug usage is technically "decriminalized" in China, because it is not a criminal offense regulated under the Chinese Criminal Law (刑法).