You're undermining your health.
4 seconds sound clip from the Reefer Madness (1936) movie soundboard.
You can hear this line at 00:29:49 in the Blu-ray version of the movie.
Quote context
[...]
- Sit down, Bill. There seems to be something wrong. What is it?
- You were always a fine student. You always had excellent grades.
- I guess the work is getting a little harder.
- I'd like to help you. But of course, I can't unless you let me.
- You're undermining your health.
- There's nothing, Dr. Carroll, really there isn't.
[...]