I've never been to China (I have been to Hong Kong, though this was when it was British in the early '90s), so I personally can't give you much advice; however, as lucky would have it, my partner lived in Beijing for about 2 years and travelled extensively through China during her stay, as well as partaking in some illict goods.
First things first- 'drugs' are different in China. Drugs are illegal, no one really takes drugs openly or talks about it- it's like stepping back into 1950s US. Yes, there are millions of junkies, but you ain't gonna see them, everything is very underground, very taboo and when you're dealing with drugs you are dealing with the deepest pits of the Chinese underworld (which is saying something once you realise that the CCP operates like the mafia). In China drugs = opium/heroin, there is a LOT of historical baggage (opium = opium wars = the west trying to destroy the middle kingdom. drugs = west trying to destroy glorious socialism with chinese characteristics- china number one!), this is particularly true of the Han. Some ethnic groups smoke cannabis/hash (Uyghurs seem to make/sell/consume most of the local hash), and this is more 'open' than other drugs, but at the same time you're dealing with all sorts of ethnic differences that you're probably not aware of- hash happens in Uyghur areas. If you talk about 'psychedelics' or 'soft drugs' no one is gonna understand what the fuck you mean- I can't emphasise this enough, the complete cultural difference in dealing with drugs. If ANY Han chinese EVER offers you, for instance, heroin you give them a lecture about the opium wars and tell them to FUCK off because they ARE trying to extort you. The CCP and the mafia are the same thing.
Ok, so you'd think that this would mean drugs = no in China. Well, no really. The culture and society is different, but China itself is essentially lawless. Like, it is an authoritarian society, you notice that the state is much more in your face and more 'there' (a lot of people in government issued uniforms doing different jobs), but the power of the central-authorities is heavily reliant on teh whim of the infinately more corrupt local politicians. This means that the laws don't apply most of the time. I mean, do you know how many murders there are in China? There is this lake in Beijing that all the bodies are dumped in because there are no security cameras in the area and it's very, very high density (shanty town)- dozens are dragged out by locals every day and none of them are investigated, you have to pay the police to investigate crimes. Maybe it's the state murdering these people, don't ask questions.
If you really want to take drugs in China my partner says the trick is to not involve any locals in your consumption. This isn't hard- firstly, you buy drugs exclusively off foreigners. Nigerians, Angolans, Somali and other Africans do the bulk of the dealing in China. You may scoff, but it's true- atleast in Beijing. Most of them are in someway related to someone with some dealings with some African embassy- their 2nd cousin is a secretary for the Nigerian Ambassator in China so they bought a visa. This is pretty safe, although many of them are more interested in marrying you (if you're a woman) or stealing your credit card. They sell cocaine (cocaine is THE expat drug), opium/heroin (quality varies more than elsewhere in Asia, you can end up with real shit unlike Cambodia where you get sand or the most fireass shit you have ever tasted), hash (quality varies HUGELY, the local soap-bar like hash is called 'battery acid hash' and is reputably bulked up with sulfuric acid, although I doubt this- avoid. It's mainly from Xinjiang and turkish/lebanese style hash, you wanna go for the blondest stuff they have- usually they have 3-4 types to pick from) and very occasionally meth (high quality crystal from Japan/NKorea/Burma/Malaysia) or 'yaba' type speed pills that they'll probably tell you are esctasy.
Anyway, RC's are irrelevant in China- yes, your powder may be completely legal, but that doesn't matter one fucking bit. If you get caught with what the police assume to be some form drug you WILL be arrested you WILL be charged to the fullest extent of Chinese law you WILL NOT recieve any special treatment and your govenement WILL NOT do a fucking thing to help you. A person my partner knows (a westerner, from Montreal in Canada- fortunately could speak very good Chinese) violated his visa, overstayed for 3 weeks, was arrested and spent 6 weeks in a labour camp about 6 hours (around 50-75km, there is a traffic jam so big you can see it from space consistantly going into Beijing) outside of beijing while being held before his formal expulsion from the country. He was deported to Hong Kong, applied for a new visa and crossed back into the PRC without issue. The way they fuck you doesn't even make sense!
I'd do it, I'd fucking love to be peaking on 6mg of DOC while all of the universe collapses in on itself while walking through a Uyghur shanty town in Beijing...but I'm a fucking idiot and compulsive risk taker. I think that you should think really fucking hard about what you're doing- unless you particularly want to experience being under the influence of drugs within a authoritarian socialist society then it's probably not going to be as great as you'd imagine. You'll probably just be paranoid as fuck and get really mopey after the 85th Han calls you a 'Fucking cunt foreigner' as a general epithet for your existance today.