This draught was a burning liquid used by the forces of the Dark Lord Sauron. It seems to have effects such as renewing the strength and warmth of the drinker and healing wounds and injuries. The Uruk-hai leader Uglúk forced some to a wounded Meriadoc Brandybuck and Peregrin Took while they were being taken from Amon Hen to Saruman the White in Isengard. Later, Frodo Baggins had the liquid forced down his throat while recovering from the wound he received from Shelob. Its colouring, along with the orcs reputation of being eaters of human flesh, implies that the draught may contain blood, human or otherwise.
In the appendices of The Two Towers, Dominic Monaghan who portrays Merry, states that the mixture he drank was made of a peach drink and SodaStream Cola concentrate.