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. Also implied by the burning sensation perceived by those who drink it, the perceived "warmth" and the numbing of pain ("healing injuries") that it may be alcoholic in some way. Real world examples of laborers and soldiers imbibing in narcotics that lessened pain and fatigue (such as hashish for the Hashishin [Assassins] of the Middle East, khat in Arabia and Africa, kava kava and kratom in Southeast Asian countries, etc) lend credence to the idea that the orcs would have some kind of substance created to give them an edge on the march or in battle.
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.