Narcan / naloxone is effective against all opioids. It's a matter of whatever else might be in someone else's system (ie benzos, tranqs) that it doesn't affect, as it blocks the brain's opioid receptors. But you should be cautious on using Narcan unless someone's breathing is either really labored (like if it's more of a gurgle than a breath) or has stopped. Otherwise it's not an opioid overdose, and if the person is a regular opioid user you'll snap them into withdrawal right away without any need to do so.

Also, for people seeing this later - please feel free to hit me up with harm reduction questions! First time long time, seeing this thread finally coaxed me into registering an account.