In the US it's legal-sorta but the NIH can't fund it and the FDA is not allowed to approve treatments based on it. So someone could do it in a research setting but there's not a pathway to market in the US (in practice people will do the first ones in a friendly legal climate like Peru).
I don't have citations to hand but I can attest that this has been the case for a long time now. There are jurisdictions that are more open to various semi-banned (either unfundable, a regulatory morass, or both) topics of research; China is famous for offering lucrative grants to attract foreign researchers of many of these.
