Im only speaking from my experience with 2 hallucinogenic drugs ( LSD, mushrooms). Unless they were using something much more potent, I honestly do not believe that many people can hallucinate the same thing, but even then, everyones mind is different, the drug is going to effect them in different ways, they WILL see things, but not the same exact things.
Thinking back, even when myself and my group of friends were using quite a lot of LSD, the hallucinations were not really that intense, its not like you would see pink elephants suddenly appearing out of nowhere, it was more like different effects on things that were already there, example, one night when I took 10 units of acid, I saw a cat jump from a couch at my GFs house, the only hallucination I saw was little sparkles around the cat that followed it around, LSD was more a mental experience than seeing things that were not there, although one time, when my friends dad was grilling us about being out late, when he was talking to us, I kept seeing little comic book type text ‘bubbles’ containing the words he was speaking…that was probably the most intense hallucination I ever experienced.
