I snooped in my son's medicine cabinet
What was the reason for snooping?
He had lied about taking drugs, so I wanted to check.
When it comes to the health of your child, sometimes privacy needs to take a backseat. It is good that you are willing to check on him, even if you breach his privacy.
I admit it's a little intrusive.
Being intrusive is better than the alternative that you don't check and something is wrong with him. You took the correct course of action here.