Many rely on an espresso from an expensive coffee shop if they need a caffeine charge for the day, but they'd be better off with a humble coffee or milk tea from a cha chaan teng.
In results that surprised a dietician, tests have found that a coffee from one of the city's trademark restaurants can contain up to six times as much caffeine as a coffee-shop espresso.
And even a milk tea can contain more than three times as much, results of the tests by the Consumer Council and the Centre for Food Safety show.
While coffee-shop espressos contained an average of 97 milligrams of caffeine per cup, with a range of 62mg to 170mg, cha chaan teng and fast-food shop coffees had on average 200mg in a range of 110mg to 380mg.
Registered dietitian Priscilla Lau Li-yi, of Holistic Nutrition Consultants, said a normal person should consume only 300mg of caffeine a day.
That meant one cha chaan teng coffee could supply the full allowance.
"I am surprised that the caffeine in coffees at cha chaan teng reach 300mg a cup. What do they put in the coffee?" Lau asked.
Even milk tea, not often seen as a big source of caffeine, contained an average 170mg, with a range of 73mg to 220mg.
Lau said this was because Chinese tea was loaded with caffeine. "The Chinese like to drink strong Chinese tea. They should know the caffeine content is high," she said.
The results showed that a person would have to buy several expensive espressos to get the same caffeine hit as from one regular coffee from a cha chaan teng.
Among the 20 coffees tested, the Golden Gate restaurant in Aberdeen topped the list with 380mg a cup.
A cup at Tsui Wah's Tuen Mun branch and McDonald's Aberdeen branch contained 220mg and 140mg, respectively.
Of the 30 milk teas tested, Lok Yuen in Kowloon City came out on top with 220mg.
Of 12 espressos tested, one from Pacific Coffee's Mong Kok branch held 94mg of caffeine while Starbucks' Kwai Chung branch had 62mg.
Lau said it would help customers if all shops labelled the caffeine content of their coffee.
She said too much caffeine would not cause chronic disease, but could lead to anxiety and insomnia.
Pregnant women and children under five years old were advised not to consume any caffeine, she said.
Dr Samuel Yeung Tze-kiu, principal medical officer with the food safety centre, warned that while there was no international standard for caffeine intake, an excessive intake could trigger a rapid heartbeat, tremors and anxiety.