When I drink lots of alcohol I get drunk. Correlation does equal causation in this instance. When I take psychedelics I see patters (hallucinations - because they are not actually there). I have seen Paisley print on my plain blue denim jeans. Just because you don't hallucinate doesn't mean others don't. I don't hallucinate without drugs (or fever). Therefore, I think it is fair to assume the the drugs are responsible for the hallucinations.