According to Andreas Moritz for people who are allergic they can use the citrate, it still will relax the ducts. You can find it in the laxative area in stores. Sorry I never used it, so I don't know the amount.
It seems you can buy it easily in America in bottles of cherry or mint flavour (at Walmart I think for example or a pharmacy) I've seen it for sale online, but for myself would be grateful if anyone knows where to purchase it (in LIQUID form - found pills & didn't like them) in the UK.
I've even experimented with mini flushes using milk of mag. but don't know how this compares and get the impression using mag.cit. is a better idea!