It happened at the CVS Pharmacy, located at 270 Main St., at 11:58 a.m.
Police say the suspect jumped over the pharmacy counter and shot an employee in the foot with an imitation air gun.
The suspect then produced a second weapon, which he used to force the employee to open a safe containing Oxycontin and stole approximately 150 pills.
The man ran out the rear of the store toward Handsome Avenue.
The suspect is described as a white man, between 5 feet 6 inches and 5 feet 11 inches tall and between 20 and 30 years old. He was wearing a hooded sweatshirt and a black scarf over his face.
No one was injured during the robbery.
Detectives are asking anyone with information to call the Fifth Squad at 631-854-8552 or anonymously to Crime Stoppers at 1-800-220-TIPS. All calls will be kept confidential.