Low Dose Naltrexone is still naltrexone. naltrexone is an opioid antagonist. like the opposite of an opioid, if that helps you understand. It probably simulates mild opioid withdrawal, since it's blocking your endorphins from binding to opioid receptors to some extent. emphasis on to some extent, since it's low dose naltrexone, what should happen is that your opioid receptors upregulate to compensate, thus causing you to be more sensitive to endorphins. This is all very approximate so I wouldn't find it odd to feel like shit for the first few days and then start feeling better, even hypomanic.