Action on Sugar is concerned people are consuming more than they should, without realising it.
The team based at Queen Mary University of London looked at hundreds of products sold in UK shops and online.
Some contained eight teaspoons of sugar in one small 250ml can.
Gin in a tin
The sweetest gin and mixer was Classic Combinations Pink Gin and Tonic, containing 27g of sugar (nearly seven teaspoons) in a 250ml can – the same sugar content as Coke.
An Archers Schnapps and Lemonade and a Malibu and Cola both contained 33g per 250ml can.
Nine out of 10 of the pre-mixed spirits and cocktails in the study did not have clear on-pack information about the sugar content within, the researchers found.
These products are not legally required to have a nutrition label on them.