The research, by a team from Otago University, is one of the first studies of such taxes in the Pacific, where 14 countries and territories have introduced them.
Since introducing its tax in 2013, the Tongan Government has taken about $US3.4 million (approx $NZ5.1m) a year in revenue.
The tax has been raised twice since it was first introduced, and now sits at about 31 percent, which led to about a 17 percent increase in the price of a particular brand of soft drink, according to the research.
