The ACTH stimulation test measures how well the adrenal glands respond to adrenocorticotropic hormone (ACTH). ACTH is a hormone produced in the pituitary gland that stimulates the adrenal glands to release a hormone called cortisol. This test is used to diagnose or exclude primary and secondary adrenal insufficiency, Addison's disease, and related conditions. During the test, a small amount of synthetic ACTH is injected, and the amount of cortisol (and sometimes aldosterone) that the adrenals produce in response is measured. This test may cause mild side effects in some individuals. Commonly reported reactions are nausea, anxious sweating, dizziness, itchy skin, redness and or swelling of injection site, palpitations and facial flushing, but should disappear within a few hours.