Cobicistat, used as a pharmacokinetic booster in therapeutic combination with human immunodeficiency virus (HIV) protease inhibitors and integrase inhibitors, is a strong inhibitor of cytochrome P450 3A4 (CYP3A4). Since most glucocorticoids are metabolized by the isoenzyme of the cytochrome P450 pathway, their plasma concentrations can be highly increased in the presence of cobicistat-boosted darunavir, with subsequent risk of iatrogenic Cushing's syndrome (ICS) and secondary adrenal insufficiency. We report a case of a 45-year-old man with HIV-hepatitis C virus co-infection treated with raltegravir and darunavir/cobicistat since 2019. In May 2021, he underwent a sleeve gastrectomy due to morbid obesity (BMI: 50.9 kg/m2) with multiple comorbidities. Four months after surgery, he was diagnosed with asthma and was started on inhaled budesonide, which was later changed to fluticasone propionate. At the 12-month postoperative visit, the patient referred proximal muscle weakness and asthenia, and suboptimal weight loss (excess weight loss of 39%) and high blood pressure were documented. Moon facies, buffalo hump, and abdominal large vinous striae were evident on physical examination. Laboratory studies showed impaired glucose metabolism and hypokalemia. Cushing's syndrome was suspected and further investigation confirmed its iatrogenic origin. The diagnosis of ICS and consequent secondary adrenal insufficiency due to an interaction between the darunavir/cobicistat combination and budesonide/fluticasone was established. Darunavir/cobicistat therapy was replaced by dolutegravir/doravirine dual therapy, inhaled corticoid was switched to beclomethasone, and glucocorticoid substitutive therapy was introduced. This is a particular case of overt ICS due to cobicistat-inhaled corticosteroid interaction in a superobese patient, developed after he underwent bariatric surgery. The presence of morbid obesity, combined with the rarity of this pharmacological complication in individuals taking cobicistat, made the correct diagnosis even more challenging. A meticulous review of pharmacologic habits and potential interactions is essential to avoid serious harm to patients.