Will taking naltrexone one time make you really sick?

No: Not usually, but everyone is different. And, there are potential side effects to this medication.

No: naltrexone blocks opioid receptors. You have no opioids in your system – it means you did not take any narcotic pain medications, heroine etc - you are not likely to have any reactions. On the other hand, we produce our own endorphins. You normally have them in response to good food, sex, pain, etc. it is very rarely happens that some people have mild nausea when they take the first dose.