A consumption of illegal drugs can be recognized among other things by a change of the pupils.
Hallucinogen drugs such as Cannabis, LSD and also atropine lead to a pupil dilation (mydriasis) as reference to a sympathetic nervous stimulation. At the same time Cannabis consumption can lead to a turning red of the binding skins, as well as with chronic consumption to a conjunctivitis (binding skin inflammation).
A simple noticing rule for the direction of the pupil change comes from O. PROKOP: Substances with the alphabetical initial letters A, B, C extend the pupil; substances with M, N, O, P as initial letters narrow the pupils.
As a general indication of intoxication light rigid pupils can be observed.