A cup of Costa coffee contains more caffeine than four cans of energy drink Red Bull, according to research from Which?.
The study found that a medium cappuccino from Costa contains 325mg of caffeine, nearly five times as as a Starbucks cappuccino, which contains 66mg.
This is also stronger than four 250ml cans of Red Bull, which each contain 80mg of caffeine.
A Costa spokesperson said: "The amount of caffeine included within each coffee varies, depending on both the coffee and size of drink ordered by a customer. All Costa coffees can be enjoyed with decaf coffee and we offer a wide range of non-caffeinated drinks including the FuzeTea Superfuzions range.
"All caffeine information is available both in our store or via our website and we would encourage customers to be aware of the caffeine content in their favourite Costa coffee to ensure it is right for their dietary requirements or lifestyle choice."
The consumer rights organisation compared the caffeine levels of espressos, cappuccinos and filter coffee drinks at Caffè Nero, Costa, Greggs, Pret a Manger and Starbucks.
Greggs and Pret A Manger came in second (197mg) and third (180mg) in terms of levels of caffeine in their cappuccinos.
Caffè Nero had the second lowest levels of caffeine in its espressos at 45mg, which is less than the typical dose of caffeine found in a tea bag (75mg).
Starbucks had the lowest caffeine levels overall, with its filter coffee range offering slightly over a third (102mg) of caffeine levels found in a Pret filter coffee (271mg).
The study advised that people who are sensitive to caffeine or those who are pregnant should avoid stronger coffees and suggested customers could reduce caffeine intake by requesting fewer shots in their drink.
Shefalee Loth, nutritionist at Which?, said: "Our analysis has shown that there are big variations in caffeine content between drinks from different high-street coffee shops. Most of the time this shouldn't be an issue but if you drink a lot of coffee or need to limit your caffeine intake you might want to consider what you're ordering and where from."