I know using dope alone is more dangerous but it's really my only option right now. I recently was able to get my hands on a narcan kit just in case, though it might not ever come of any use. Are there any signs you might end up overdosing before you lose consciousness that I should be aware of? Has anyone ever self administered after they knew they took a bad or really strong shot?
From everything I know..... Orally, if it's not your first time, you might know, and would have a little while. Shooting, you might know, for just long enough to think "shit". Then the only way you know more is IF you wake up. I don't think you stand a snowball's chance in hell of saving yourself from an injected OD.
If you were going to overdose, you likely wouldn't be in a position to grab the Narcan kit and self administer the Naloxone. You would be way to intoxicated and going in and out of "nod-land". So it would be best to not shoot up alone if you are not a long-time user. Is insufflation possible with the heroin you have?
If insufflation is not possible or desirable you could administer rectally. Morphine has a GREAT effect rectally so I would assume heroin does as well. That would likely be the best ROA other than shooting.
If injecting after you register only push down part of the way on the syringe and then wait a few seconds before injecting the rest that way you will be able to tell if your already way to high before injecting the full shot. This is obviously not a full proof method but it will decrease your chances of over dosing. Using IM or SC also gives less of a chance of having a fatal overdose as the drug is absorbed slower then IV, but there is an increased risk of infection when using IM or SC.