Acai Berries from the high street?

I've bought a free trial of Acai berries and Hoodia tablets and I love them. I've lost so much weight. I wondered if buying them from high street stores such as Holland and Barrett would have the same effect as the ones I have got now? I've heard that the high street brands are not the same product and don't work well, but they are a lot cheaper. Does anyone know if this is true?