The Finnish makers of mushroom coffee, Four Sigmatic, claim to offer the same caffeine kick without the apparent side-effects of the regular stuff.

And while it may sound, frankly, revolting, reviewers have said that it is “rich” and “mellow”, and like a mix between tea and coffee. Tero Isokauppila, the founder of the firm, told Food Republic that while people may raise eyebrows at the idea of mushroom coffee now, he hopes it'll be as commonplace as eating rash fish.

Four Sigmatic claim that their “medicinal mushrooms” – which aren’t anywhere near a dodgy as they sound – boost brain power and increase productivity without the side effects that some people experience.

The process involves liquefying and then drying different types of mushrooms to make an extract which is mixed with regular coffee. The maitake mushroom blend is believed to help regulate blood sugar levels, while the alkaline chaga mushroom counteracts the acid of coffee that can cause upset stomachs. A similar process goes in to their mushroom elixirs (whatever that means) and cocoas.

However, Cynthia Sass, the nutrition editor of warned that while some research indicates that mushrooms have health benefits, it's best not to try to recreate the coffee at home. Maitake muhrooms taken on their own can interact with medication used to thin the blood or control blood pressure.

“It’s also important to note that chagas have a blood thinning effect, so they shouldn’t be consumed before any surgery,” she said.