If you suspect that someone close to you is intending to intoxicate a person without their knowledge, you can try to raise their awareness about the seriousness of what they are about to do, but don't put yourself at risk.
If the person is a stranger, or if the situation appears to pose a danger to yourself or others, call 9-1-1.
If you are concerned for the safety of someone who is exhibiting one or more symptoms of severe intoxication, call 9-1-1 and stay with that person until help arrives.
Don't hesitate to ask for help, even if you've consumed or are in possession of an illegal substance. There is a Federal Law protecting good Samaritans who provide assistance to a person in danger.