Thanks for the query,
It appears to be a fixed drug eruption
He might have developed a reaction to bupropion
A photograph would have helped me in giving a closer diagnosis.
Ask him to apply a mild steroid cream like fluticasone
This will give him relief.
Please meet a dermatologist
for exact diagnosis.
A change in drug might be required.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.