Regime can be referred to any Government or Governing Authority or character of a prevailing social system.
Regimen is referred to a system of treatment or a systematic diet plan for any therapy or medicine.
Pakistan had been under military regime for many years.
Military regime has never been successful in most of the countries.
North Korean regime is adament on making nuclear weapons.
Regimen: The doctor has advised him to follow a strict dietary regimen.
The cancer patients are generally treated by Chemotherapy regimen.
Antibiotic regimens are prescribed by doctors to treat bacterial infections.