I highly doubt it was really ISIS who produced the drugs. I've actually done a lot of research on the captagon trafic and while it is true that, at some point, ISIS members were involved in it, most of the captagon in the Middle east is produced by Hezbollah in the syrian-lebanese border. Most of the pills are then sent to Saudi Arabia where Captagon is a popular drug.

In order to send it to Saudi Arabia, Hezbollah have to use tribal smugglers in Syria and Iraq or go through a turkish port but either way they have to use syrian smugglers and that's where ISIS appear. So there's a kind of unholy alliance between two enemies (ISIS being a sunni radical group and Hezbollah are a shia radical group).

I've read the article in La Reppublica this morning and i think the Italian police said it's ISIS because it is well documented that Captagon is associated with ISIS and it's a good publicity stunt. They went as far as saying that the pills have two semi circles on them which is the "brand" used by ISIS. That's far fetched.