"Legalize" implies we need permission from the government to control what we put into our own bodies. That doesn't really make sense in a free country.
"Decriminalize" makes more sense: it rightfully implies the government screwed up when it outlawed the substance(s) in the first place...
IMHO banning chemicals is
a) impossible from a practical level because there are infinite chemicals and no means to enforce their use
b) misguided since politicians are unqualified to assess the various technical aspects of medicinal chemistry
c) counterproductive because when something people use is banned, they turn into criminals and the end result is a black market which encourages people to ignore other laws which actually DO matter (like when folks commit murder related to drug deals -- if the drug were not criminalized, then there would be no need for a black market drug deal)
TLDR: Don't legalize it. Decriminalize it!