That is just the first Google hit.
https://knowledge.wharton.upenn.edu/article/is-portugals-dru...
The prediction (at the time) by those against the program was that Portugal would become a giant Amsterdam, and drug tourism would rise and the country would be awash in drugs and drug users.
None of that happened. We are still around or below European averages.
Isn’t this consistent with decriminalization that people aren’t afraid to talk about past drug use? You see similar statistics with, say, people coming out of the closet when homosexuality is decriminalized; which conservatives like to paint as “legalization making people gay”. The OD cases could also be from people more readily calling for help rather than trying to cover up.