If you read Stan's Sn protocol (in resources) he was an advocate of using milk of magnesia which is a laxative instead of tagamet on the day of. Not for the purpose of what you want it for, but for something to do with stomach ph or HCl, I can't recall now (there's a thread somewhere explaining it, just search MIlk of magnesia,) but my point is if he thought it was okay I would trust it. He put tons of research into it and was a very smart man. Therefore, I would surely think taking it the day before for your purposes would be okay, but please do your research, I'm just relating the bits of info I happen to recall.