If given at the wrong time, the Subutex or Suboxone your doctor has given you to treat your Opioid Use Disorder could cause you to go into withdrawal. For that reason, it is really important that you get professional advice on exactly when to start taking your prescription. Subutex's brand labelling indicates that you should wait at least 6 hours since your last dose of heroin, morphine or OxyCodone, or at least 24 hours since your last dose of methadone, prior to taking any Subutex.
These timings are based on estimates of how long it will take these substances to stop having an effect on the body. However, the advice that doctors usually give is that you should already be at least slightly in withdrawal from the opioid you have last used before you initiate Subutex or suboxone. This time can vary greatly depending on your metabolism, the duration of your opioids use and the size of your dose.
When you go to your doctor or healthcare professional, best practice dictates that they should assess you using something called the Clinical Opiate Withdrawal Scale (COWS). This will help them determine if you have entered withdrawal enough to go onto a dose of Subutex without getting sick. If you score higher than around 5 or 6 on that scale and demonstrate enough withdrawal symptoms, you are good to go.