Before starting your journey with naltrexone, make sure to get the following tests done.
1. Liver function test
2. SADQ test to measure the severity of your addiction.
If your liver function test comes out to be severly abnormal then naltrexone may not be the right medication for you. In that case, acamprosate may be a better option as it is extracted through kidney while naltrexone is metabolized through liver.
If the severity of your addiction is too high then you shouldn't start naltrexone or the sinclair method. In that case you need to do an inpatient detox first.