@carolinemartin656 I use drugs.com as my go to site to check for any drug interactions.

I keyed in interaction between Imuran and Naltrexone. According g to this site, there is no drug interaction between the two.

I find if in doubt, your local pharmacist is the best source of information. If you use a regular pharmacy for all your medications, that pharmacy would have your list of medications too, so would be able to advise you.

After working as a unit clerk in a hospital I have developed a great respect for pharmacists and nurses - they more often than not know more about drug interactions than the prescribing g doctors! Check with your regular pharmacist!

In the meantime here is what I found about any interaction between Imuran and Naltrexone - but check with your pharmacist anyway.
https://www.drugs.com/interactions-check.php