While an XL might be a tad much, a normal one isn't enough, so if worms are an issue, it is much better to give them a tad too much than not enough, as not enough wont kill all the worms, although if it is just a preventative, then it may be OK. Luckily for me, both girls are under 4kg, although they get Milbemax as I can't use Drontal.