I have written before about coffee, and that I try not to take away their morning cup of coffee from most clients. There are even many health benefits that have been studied, and coffee drinking is associated with longevity. However, I do urge moderation and caution, especially for those with chronic exhaustion, for whom a switch to decaf or coffee alternatives may be best.

However, for many people, drinking strong coffee on an empty stomach first thing in the morning may be a bit rough- on the stomach, and on the adrenals. Often when we get up in the morning, if we don't eat within an hour or so, adrenalin will kick in to maintain steady blood sugar. 

Adding coffee (caffeine) to that, especially black and sugar-free coffee, means the adrenals will be really stimulated. While that may make us feel ready for the day, it's not so good if we are already having issues with chronic stress or exhaustion.

One way to ameliorate this is to have your coffee milky with sugar. This balances the adrenalin effect. Sugar calms adrenalin. The fat and calcium in milk or milk or milk alternatives also help slow down the absorption of caffeine. 

The other way is to have your coffee with breakfast. Then the other food will help balance and you don't get that strong adrenalin spike but you do get a more gentle stimulant effect, along with the health benefits. I do recommend some simple carbs such as sugar, honey or fruit with breakfast though and with your coffee, to support the adrenals. 

If you would like to read more about the benefits of coffee, here is a good article: http://raypeat.com/articles/articles/caffeine.shtml