Other sweet drinks, such as Lucozade and Ribena, have slashed their sugar content to avoid the tax, and consumers are complaining that old favourites now taste vile.
Shortly after the 2016 announcement, Lucozade Ribena Suntory launched Lucozade Zero in the United Kingdom, citing "the nation's changing health agenda".
Funds raised by the sugar tax will be diverted into school sports, the Government insists.
Clark wants the government to introduce further measures, including reducing sugar, salt, and fat levels in everyday foods, ending price promotions for unhealthy food and drink, and restricting junk food ads on TV before 9pm.
The sugar tax has added 10p to a typical 330ml can of Coke or Pepsi.
"It's upsetting to see so many children admitted to hospital with tooth decay, but swapping out sugary drinks could be an easy win for busy families", said Dr Sandra White, dental lead for Public Health England.
Image There are 36g of sugar in one can
It is hoped the tax will encourage drinks companies to cut down on the amount of sugar in drinks, and consumers to choose lower sugar alternatives.
The reduction in sugar was large: Fanta Orange saw a 33% decrease, Fruit Twist went down by 25% and the lemon flavour saw the biggest drop with a 46% decrease in the amount of sugar in a bottle. The research found that low sugar content now stood out as the single most important factor consumers looked for when seeking out healthy food.
Coca-Cola Great Britain said: 'There is no evidence from anywhere in the world that shows taxing soft drinks reduces obesity rates.
Though there has been a great deal of enthusiasm for the levy, which was welcomed in a notable cross-party consensus when George Osborne put it forward in his Spring Budget 2016, there have been voices of dissent claiming it would do little to impact the high rates of childhood obesity the United Kingdom experiences.
It is also expected to raise more than £275m per year for the Treasury. It is the most common reason for children aged 5 to 9 to be admitted to hospital, causing 60,000 missed days of school each year.
Tesco said it would continue to stock a full range of branded drinks, which could be more expensive or come in a smaller serving size, but estimated 85% of all the drinks it sells would be exempt from the levy.