Internist doctors or internal medicine doctors are doctors who specialize in the diagnosis and medical (nonsurgical) treatment of adults.
They do treatment of patients and adults only without surgical treatment and only with medicine and the internal medicine doctor can can prescribe medicine for treatment.
Internist medical doctors also provide long term and comprehensive care and manage both common and complex diseases.
Internist doctors are just specialists in treating adults and not children like a family physician would treat both adults and children.