Most cops are trained to spot drug users and visually identify what they're on based on how they act, identifying signssuch as track marks and burns, and the look of their face and skin.
But nothing gives a drug user away like their eyes, because drugs tend to do funny things to a user's pupils.
Amphetamines, cocaine and marijuana enlarge the pupils, and smoking pot also tends to make your eyes bloodshot red, while opioids like heroin constrict the pupils.
But can you actually tell which drugs someone is on simply by looking at the size of their pupils?
Vice visited a bunch of nightclubs in Berlin and snapped pics of people's eyes so they could see if the pupil test is a myth or the ultimate identifier of a drug user.
Their photos show you really can't tell what will happen to a user's pupils once they've taken drugs, because other factors like epilepsy, cataracts and sensitivity to light can affect the pupils as well.
Which is why medical professionals from the Charité Hospital in Berlin say the bottom line on the pupil theor is this:
It's absolutely not possible to tell what drugs someone has consumed by looking at their pupils.
-Via Vice