Fentanyl is now mixed into counterfeit pills and other street drugs, often without the person taking them knowing it is there. That changes what you are watching for. Someone can be exposed after using a substance they believed was something else entirely, which is why the signs matter even when fentanyl was never the intended drug. Learning what to look for in yourself or your loved one, and acting early, is one of the clearest ways to prevent an overdose before it happens.