[1] Because acne is generally a disorder of the pilosebaceous units caused by hormones, the medications that trigger acne medicamentosa most frequently are hormone analogs.
It is also often caused by corticosteroids; in this case, it is referred to as steroid acne.
[2] Other medications can produce acneiform eruptions (usually pimply bumps and pustules that look like acne).
[3] Some conditions mimic acne medicamentosa.
The most common mimic is folliculitis produced by an overgrowth of the Malassezia species, often secondary to oral or systemic corticosteroids, or secondary to broad-spectrum antibiotics such as the tetracycline family used in acne.