80's Movie Poster Has Evil Doctor Holding Drill

by Noril
(Philippines)

I've been trying to find this 80's horror film about a doctor who performs horrid experiments on people.

In one scene, he drills a hole in the patient's head and injects him with liquid insects. In another, he drugs a teenage boy while he's taking a shower, operates on him, and then the boy goes and shoots his parents.

The movie poster has a doctor wearing an operating mask holding a drill. I thought the title was 'Doctor Evil' but that's not the right film.

I hope you can tell me the title of this flick. Thanks!