UPDATE: Grange Pharmacy owner Jane Riley described last night�s arm hold up as �quite a shock�.
The two staff members who worked last night were taking time off and the pharmacy may review its night security measures, including the possibility of keeping its doors locked.
The pharmacy trades until 10pm.
�The two girls that were in the store were quite shaken up,� Ms Riley said.
�We haven�t had an incident for many years, eight or nine years.�
The pharmacy has a duress alarm to alert security personnel and police were called.
It was reported earlier that Grange Pharmacy in Cooloongup was the target of an armed hold up.
About 9.20pm last night, a man entered the pharmacy on Grange Drive wearing a balaclava and allegedly armed with a knife.
He approached the counter and demanded the shop assistant fill a bag with money, then walked around the back of the counter and demanded drugs.
The man left in an unknown direction with a small amount of cash.
He is described as fair skinned, about 165cm tall, wearing a black three-hole balaclava, baggy fluorescent yellow hi-vis jacket, black trousers, and grey sneakers.
Police are calling for anyone with information to call Crime Stoppers on 1800 333 000.