The answer is both.
Adrenal Fatigue is not a term used in conventional medicine. It is a layman's term often erroneously used to describe physical states that have nothing to do with the adrenal glands. It is for these two reasons (not a term used in conventional care and misused by laypeople) that it could be considered bogus.
In order for Adrenal Fatigue to be a real condition it would need to satisfy two criteria:
low hormone production (subclinical) from the adrenal glands
causation of hypofunction preceded by taxation
Each adrenal gland has an inner medulla and an outer cortex. Both sections produce hormones in response to stress mediated by the sympathetic nervous system. More stress = more hormone production. This point is not controversial.
Over two dozen hormones are synthesized by the adrenal glands (Anatomy and Physiology, Marieb, pg 626). Chronic low production of adrenal gland hormones is called Addison's Disease and it is not caused by overstimulation or taxation. However, can there be low production of any adrenal gland hormone without it being pathological? In other words, can there be a subclinical drop in adrenal gland function resulting in one or more adrenal gland produced hormones to fall below optimal levels? The answer is absolutely yes. Can this drop follow or be caused by overstimulation of the sympathetic nervous system? Also, absolutely yes.
These hormone levels can be tested medically. They typically are not tested because there is no treatment based on drugs or surgery. Abnormal hormone levels will result in symptoms to the patient but, unless the doctor is trained in corrective physiology, the symptoms will be treated not the cause.
Let's take for example cortisol. Consumption of stimulants will result in an increased production of cortisol. High intake of stimulants will eventually lead to exhaustion. This spike and drop can be measured through saliva tests and validated medically. However, the term Adrenal Fatigue is never be used. It is referred to as high or low cortisol levels. In this case the term Adrenal Fatigue is technically correct even though it's medically out of style.
As with any trend or fad be careful what you read. Adrenal Fatigue, although sometimes an accurate description, is a terribly misused term. Guessing or generalizing about your health is never a good idea when there could be serious issues needing treatment. When in doubt, seek a doctor trained in corrective physiology.
Holistic & Integrative Medicine