Nope, I will have to disagree. There is plenty of physical evidence of weed in Europe.
The earliest physical evidence of weed Ever was found in modern day Romania, no doubt as it was the eastern most part of the Mesopotamian empire whose western most regions included india where weed was quite common for spiritual and medicinal purposes.
Furthermore, Greek scholars describe their Thracian neighbors ( ie. Modern day bulgaria, Macedonia) throwing a plant on a fire and inhaling it's fumes that would cause them to dance and shout the whole night. Homer also references a plant that is most likely marijuana in the illiad.
You're right the romans consumed weed but they didn't just use it in food, it has been documented as a medicine for them as well which indicates they took advantage of it's psychoactive properties.
As for the middle ages there isn't as much evidence, mostly because of the prominence of the catholic church and it's position on mind altering substances.
However, there is an Italian journal written by a clothes maker during the renaissance that extolls the virtues of marijuana and is evidence of it's prominence throughout Italy. The journal describes not only cannabis' textile value but it's recreational value as well.
Essentially what I'm saying is that weed has been globally proliferated for millennia. If there was a lull in it's popularity (or more likely, simply a lull in it's documentation) it is trivial in the broad scope of things.
