A passerby managed to detain an armed robber until police arrived at a Kenwick pharmacy yesterday.
A man entered the chemist on Belmont Road about 3.50pm wearing a motorcycle helmet.
He threatened staff with what appeared to be a blood-filled syringe.
He demanded drugs and left the store but was grabbed by a customer outside the store.
Police arrived and took the man into custody.
The 28-year-old Maddington man will appear in the Perth Magistrate's Court today charged with armed robbery.