Magnesium has always been a key factor in reducing tics for my son and he has used various forms of it over the years but never use magnesium oxide as it is very poorly absorbed. One really needs to find the chelated form that works best for the individual. We liked magnesium taurate, as taurine is also helpful for tics.
He started the P5P form of B6 on recommendation of his Integrative physician, as it was explained it helps much in neurology and also assists increase functionality of other supplements.
He still takes these key supplements.