A middle-aged man who collapsed and turned blue during a boozy night turned out to have ingested a bottle of amyl nitrite after mistaking it for an energy drink, a UK doctor reports.

While the cause of severe methaemoglobinaemia was initially unclear, Dr Patrick Timmons from Queen Elizabeth University Hospital in Glasgow, Scotland said the case highlighted the importance of “swift recognition and treatment” of the life-threatening disorder.

The patient, in his late 40s, had been out drinking with friends when he decided to buy a caffeinated energy drink between venues.

But after ingesting the entire contents of the bottle, he collapsed and fell unconscious.