Gaviscon Advance sold in the UK is not an antacid or at least not a very strong one. It is a reflux suppression medication designed to keep stomach acid from coming in contact with you esophagus, throat, larynx, etc. The raft shield you from the acid and allow you to heal if you have reflux. Gaviscon Extra strength sold in the US is an antacid liquid designed mainly to neutralize acid and at the same time put a thin coating in you throat and esophagus. These are totally different products and they work differently.