The Old English Pharmacopeia, known alternatively as the Old English Herbarium Complex, is distinctive among the Old English medical corpus for occurring in multiple manuscript copies. The manuscripts containing the Pharmacopeia date from the late tenth to the twelfth century. Most prominent among these is BL MS Cotton Vitellius C. iii, which, although damaged during the Cotton fire, is generally legible and contains beautiful illustrations. This manuscript has been used as the main text for the two published editions of the Old English Herbarium (first Cockayne's edition in the 1860s and, more recently, De Vriend's edition for the EETS series). Other copies of this text occur in Bodleian Library MS Hatton 76, whose version of the Pharmacopeia is closely related to the Cotton manuscript (although containing empty spaces intended for illustrations), BL MS Harley 585, which contains the oldest version of the text and also the only extant copy of the Lacnunga, and BL MS Harley 6258b, which dates from the twelfth century and is the latest extant copy of the text. The fact that we have four separate complete editions of this text clearly testifies to the importance and popularity of this medical compilation in the late Anglo-Saxon period.

This work differs significantly from the other medical collections extant in Old English. The Lacnunga, Bald's Leechbook, and Leechbook III share basic structural similarities; each appears to aspire (to varying degrees) to follow a head-to-toe organisation. Additionally, each of these three collections contains cures drawn from a large variety of different medical texts, ranging from the works of Pliny or Dioscorides to Late Antique medical authors such as Marcellus. As we have seen, all three of these works also share entries apparently drawn from a pool of pre-existing remedies circulating in translated form, some of which are shared between two or more collections. These works can be aptly called ‘compilations’ as they bring together pertinent information more or less irrespective of source. In this sense, these texts are entirely different in character from the Old English Pharmacopeia.

The Old English Pharmacopeia is formed of two halves, the Old English Herbarium and the Medicina de Quadrupedibus, respectively.