Anabolic-androgenic steroid (AAS) use is becoming an emerging public health crisis, with an estimated three to four million Americans between the ages of 13 and 50 reporting AAS use. The phenomenon is commonly associated with professional athletes but has now spread to individuals in schools, gyms, and even the military. Risk factors include being male and athletic, as well as having body image disorders like muscle dysmorphia. Anabolic-androgenic steroids are synthetic analogs of the male hormone testosterone and can cross the blood-brain barrier, influencing the regulation of several different neurotransmitters like dopamine, serotonin, GABA, and glutamate. AAS dependence can lead to both tolerance and withdrawal symptoms due to these neurotransmitter dysregulations. Chronic AAS use can lead to medical comorbidities such as cardiovascular disease, thrombotic events, secondary hypogonadism, and various musculoskeletal or dermatologic sequelae. AAS users also exhibit increased aggressiveness, comorbid depression and anxiety, and other substance use disorders. This chapter summarizes the pathophysiology and clinical features of AAS addiction, hoping to assist providers in identifying this pathology and increasing their awareness to prompt further study.