Acne On Back And Shoulders

Patient: Hello doctor.i have acne at my back and shoulders. i show it to my doc. and he suggested me to take these tablets.isotretinoin capsules BP20 mg , zeethrom 500mg , benzoyl peroxide microsphere gel5.5% .these tablets help me alot in reducing acne now my back is almost i just only want to know that what is happened to my body that the doctor gave me these tablets for treatment . and also is acne came again after i stop taking the medicine??thank you