A 17 year old girl had been taking a drug for the treatment of acne for the last 2 years, which has lead to pigmentation. Which drug could it be?

Both minocycline as well as chlorpromazine can cause pigmentation on long-term use. However, as the patient in question is being treated for acne, the answer should be minocycline. Antibiotics used in acne are erythromycin, clindamycin, tetracycline, doxycycline and minocycline.