The honest answer is: it depends entirely on the brand, and a lot of them don't tell you.
Why the answer varies so much
"Mushroom coffee" describes a very wide range of products, and they don't all contain the same amount of coffee.
Some are blends that replace part of the coffee. If a product is 50% coffee and 50% mushroom powder by weight, a scoop contains roughly half the caffeine of a scoop of coffee. Some brands do this deliberately and say so. Others do it and don't.
Some are instant powders, where the dose per serving depends on how much powder you use and how finely it's been processed.
Some, like ours, are ordinary ground coffee with functional ingredients added rather than substituted. The caffeine is whatever the coffee brings.
That's why you'll see figures ranging from about 40mg to over 100mg per cup across the category, all sold under the same two words.
How to read a label that won't tell you
If a product doesn't state caffeine content, three things are worth checking:
Does it list the coffee amount per serving? If not, you can't work it out.
Does it say "coffee blend" or similar? That usually means the coffee has been cut with something.
Is it instant? Instant is generally lower in caffeine per serving than ground coffee, though it varies.
What ours is
MyCelia is full-strength coffee. We don't cut the caffeine and we don't replace part of the coffee with powder — the chaga and L-theanine are added to the coffee, not swapped in for it.
So expect roughly what you'd get from a standard cup of ground coffee brewed at the same ratio. Two tablespoons per 8oz is our measure.
Each serving also contains 100mg of L-theanine, the amino acid found in green tea.
If you're sensitive to caffeine, treat this the way you'd treat any full-strength coffee. That doesn't change here.
The ratio matters more than the brand
Whatever you're drinking, how you brew it moves the caffeine number more than most people expect. More grounds, more caffeine. A longer brew, more caffeine. If you want a lighter cup, use slightly less coffee rather than looking for a lighter product.