Agree with the above. I don’t know if it’d make it too clunky, but could try including a why they test it on the friends, E.G. In an attempt to fend off competition a backyard drug cook secretly tests a new drug on his friends, but must survive their attacks when it turns them all into zombie like savages.

Like I said that isn’t perfect, but I think testing it on unwilling or unknowing people means they’ll be more desperate to save them as they never knew what they were getting into.

Hope that makes sense and helps. Overall I like the idea, as the hallucinations could be played up to kelp you guessing if they have taken or has. The protagonist and he is huntin them.