One of the options available on the Holland & Barrett "Buy 1 Get 1 for a Penny" deal. Seems to have good reviews so worth a try if you happen to have one too many shandies at the weekend. Free C&C as well!
Overhang Revitalising Drink (for Hangovers!) Buy 1 get 1 for a penny (£2.50 for 2) at Holland & Barrett - Free c&c