One should compare against other countries that didn’t change their laws.
Increased use could be explained by increased availability that is independent of legality (eg: better smuggling routes or larger synthetic batches).
Anyways, reduced opiate use and increased use of the other drugs mentioned generally sounds like a win to me.
I’d also consider more widespread recreational use by previous non-users. I’m not sure if that’s a problem for the lower-dependence risk drugs mentioned.
In Germany, which didn't change its laws, prevalence of drug use fell during the same period.
Also note that it's significantly reduced opiate use among youth (15-34 y.o.): total opiate use only went down a little, which means that it likely has increased among people over 35.
Point is, even if overall drug problems decreased in Portugal (which is not clear to me at all, since total drug use increased), evidence that it's the decriminalization that helped, is flimsy at best.
Increased use could be explained by increased availability that is independent of legality (eg: better smuggling routes or larger synthetic batches).
Anyways, reduced opiate use and increased use of the other drugs mentioned generally sounds like a win to me.
I’d also consider more widespread recreational use by previous non-users. I’m not sure if that’s a problem for the lower-dependence risk drugs mentioned.