The robbery took place the morning of July 1 at Harry's Pharmacy on South Broadway.
Police say a man with a handgun demanded Oxycodone from a male employee.
The suspect walked behind the counter and ordered a closed cabinet to be opened.
After obtaining several bottles of narcotics he fled on foot northbound on Broadway towards Roosevelt Street.
Two employees were in the store at the time but were not hurt.
The suspect is described as a white male, 25 to 30 years of age, medium build, wearing a bright yellow jacket, dark baseball cap, white surgical mask and gloves.
Anyone with information is asked to contact Nassau County Crime Stoppers at 1-800-244-TIPS.