Just to clarify, I didn't mean discovered around the turn of the century. Just like, no changes before then.
Well there is a huge difference between chemicals that were synthesized and knowing their potential usefulness as drugs.
Here is a rough outline I came up with for an alternate take on drugs:
As mentioned before one potentially interesting drug was GHB. It was indeed first successful synthesized in 1874 by Alexander Zaytsev (Professor at the Kazan University) but that doesn't mean that an Hofmann like accident can't happen much later. Say it happens in 1900. For some experiment Zaytsev makes some GHB again an discoveres its positive properties. Happy to have found something to give him some relief from the downsides of old age, he continues experiment with the drug. Word about these activities reaches the former head of the Kazan Psychiatry Department Vladimir Bekhterev. He experiments with GHB as alcohol addiction treatment and finds to his surprise that it not only works fairly well but is also a powerful anti-depressant. The first of its kind to be precise. Thus an early kickstarts of psycho and -neurpharmacology as well as psychiatric medication.
The next opportunity would be MDMA. MDMA was first synthesized in 1912 by Merk chemist Anton Köllisch. At the time, Merck was interested in developing substances that stopped abnormal bleeding. MDMA itself was a intermediary product but its medical properties were studied in OTL 1927. Lets say that Köllisch investigates MDMA, just to be sure there is no opportunity missed. He finds that it has similar properties to GHB also still not quiet the same. This could get
Georg Honigmann involved who established a nerve clinic in 1913 treating among other things (mostly work related) PTSD. As it happens MDMA seems to be quiet helpful with
treating just that.
Now you have German veterans taking MDMA (ecstasy) and a well known and the simple to make synthetic drug GHB during prohibition in the USA. I think both should be able to make a difference, one way or another.