(The Book of Holy Medicines) is a fourteenth-century devotional treatise written by Henry of Grosmont, 1st Duke of Lancaster around 1354. It is a work of allegory in which he describes his body as under attack from sin: his heart is the castle, and sin—in all its forms—enters his body via wounds, and against which he begs the assistance of the necessary doctor, Jesus Christ. It exists in two complete copies today, both almost identical in language although with different bindings. One of these copies is almost certainly a surviving copy from Grosmont's family, although their provenance is obscure.

Grosmont was one of the wealthiest and most powerful men in England at the time. A close companion of King Edward III, he was a major figure in the early years of the Hundred Years' War and a renowned soldier. He was also conventionally pious and able to put his wealth to demonstrate his piety, for example in the foundation of St Mary de Castro, Newarke, in Leicester Castle. Le Livre de Seyntz Medicines combines both elements from Grosmont's life, and the work is noted for the breadth of its imagery and imagination, much of which is taken from his own personal experience. The work describes Grosmont—a self-acknowledged sinner—talking directly to Christ, who is portrayed as a physician for the physically sick, and who is accompanied by the Virgin Mary as his nurse. Through metaphor, symbolism and allegory Grosmont describes how his body has been attacked by the seven deadly sins which now permeate him and talks his reader through the necessity for confession and penance to allow Christ to perform his work.

Le Livre was probably written at the urging of his friends and relatives, for a literary audience which would have primarily comprised his fellow nobility, but would also have included senior ecclesiastics, lawyers and the educated mercantile class. Historians consider it to be one of the most important domestic manuscripts extant from the era, not least due to the status and position of its creator. It exists today in a number of manuscript forms and is used by historians not only as a source for the history of books and literacy but also for the broader social and religious conventions of the English nobility.

Le Livre de Seyntz Medicines Henry of Grosmont's devotional-medical treatise is notable for being one of only a few written by individuals of such rank and power in the Middle Ages, and, to the historian K. B. McFarlane it is "the most remarkable literary achievement of them all" for the period. William Pantin concurred, writing that it was, to him, "one of the most interesting and attractive religious treatises of the period, and especially remarkable as the work of a devout layman". Antonia Gransden has described the piece as "an allegory on the wounds in Henry's soul, discussing the remedies to be supplied by the Divine Physician and his assistant, the Douce Dame", all the while interspersed with personal reminiscences of how he sinned in the first place. Arnould places it within the genre of the Confessions, as well as "the prolific literature of sin". Grosmont sententiously informs the reader how he wishes that when he was young he had "as much covetousness for the kingdom of heaven as I had for £100 of land". He blames those parts of his body which he later accuses of sin: his feet are guilty, for example, of being unwilling to allow him on pilgrimage yet being willing and able to bring him wine. Robert Ackerman has noted that, while Le Livre is an exceptional piece of work in its field, the field is a crowded one, arguing that "moralistic and confessional writings...were produced in overwhelming profusion. Duke Henry could scarcely have found a more time-worn topic and method of treatment when he penned his allegory of the sins and their remedies."

It stands out from both of these categorisations due to its highly personal, almost autobiographical tone, and avoids being merely an exemplum by the images of everyday life—"and finding in everyone a wealth of 'mystic' interpretations"—with which he illustrates the work. Contemporaries understood that to cleanse the soul, one required self-knowledge; this was only obtainable after lengthy, close examination of the self, as Le Livre does. Grosmont states at the beginning that he had numerous motives for writing the work, but the most important was to "make use of times which were wont to be idle in the service of God;" in other words, following the church's dictum that the devil makes work for idle hands. The lengths of paragraphs would appear to reflect the amount of time the author had to work on that section each day, rather than reflect any pre-planning. Structurally, the book is divided into two portions. The first describes the sinner's body, with its wounds of sin, while the second explains the spiritual cures and holy medicines necessary for its healing.

Composition Arnould describes the surviving Stonyhurst copy as being written in a bold, clear hand with each paragraph represented with a large gold initial in a textualis hand. This is accompanied by red and blue ornaments and numerous of his escutcheons and seals. The title, suggests Catherine Batt, maybe a play on that of an earlier text by Matthaeus Platearius, which title in French was . The title is placed just before the explicit. The book is written in the second person, personally directed to Christ in what Pantin calls a "very personal and affectionate way". The prose is not universally popular however; Kaeuper moans that "I fear that some readers who struggle through its turgid prose and allegory gone to seed—244 pages in Anglo-Norman French—may think it penance to read", while Fowler argues that it is "not remarkable" and even Arnould says that in places it is "laborious". It has occasionally been questioned whether Grosmont was the brains behind the work, or whether he had an amanuensis—something he denies in the text—for example, Dominica Legge suggested that this was most likely to have been Grosmont's confessor and that if he could be identified, so would the source of the text's "peculiar quality". Although possibly written by a scribe, Grosmont provides a postscript, including his name written—comments Arnould, "in a naive device prompted by his humbleness"—backwards anagramatically:

The book was composed, Teresa Tavormina suggests, "at the urging of friends" of the duke, possibly including the Minoresses of Aldgate, whom he is known to have favoured—or at the instruction of—his confessor, around 1354. In his opening remarks he says—"shades of a modern author's acknowledgements", comments Labarge—that they should receive equal credit with him for any benefit the book brings. This was a protracted, and probably not easy, exercise for the duke, as whatever his education he had not been brought up in the expectation of ever facing such a task. It is also unlikely that he was in a position to devote any length of time solely to the book's composition; although during this period war with France and Scotland was at a lull, a parliament took place at Westminster between April and May 1354 which he attended. He would also have had much business to attend to connected with his diplomatic mission to Pope Innocent VI in Avignon that October and diplomatic negotiations with Cardinal Guy of Boulogne before then. Tavormina surmises that it was composed in the months either side of Easter, with daily additions. Comprising self-reflective, spiritual assessments, as well as religious contemplations on Christ and the Virgin, Grosmont wrote both for his own genuflection and others' edification. A means of focussing himself on Christ's sacrifice and keeping him from sin, it served as an alternative to traditional forms of devotion, such as prayer.

Grosmont's focus on mortality reflected a renewed interest in the topic which had appeared in the years following the Black Death in 1348 and sporadically since, with a concomitant emphasis on penance regardless of social status. The Bible made it clear to the nobility that, whereas the poor were almost certain to enter heaven, the rich had no such guarantees, and as such the Black Death may have made a more intellectual impact on the aristocracy than the lower classes.

Sins of the author The book is structured so that the reader receives an overview of Grosmont's self-view before opening himself up to "the Divine assistant and his Assistant", the Douce Dame. He states that when he was younger, one of his chief sins was that of vanity, stating that "when I was young and strong and agile, I prided myself on my good looks, my figure, my gentle blood and all the qualities and gifts that you, O Lord, had given me for the salvation of my soul".  But pride was not confined to himself: he was proud of the richness of his possessions, whether finger rings, shoes, or armour. Likewise his dancing skills or his dress, and much as he flaunted himself he liked, even more, to be praised by others for these things. He also confesses to the sin of sloth, which beset him to such an extent that he regularly failed to rise in time for morning mass, and gluttony, with overindulgence in the best food and drink, with its rich sauces and strong wine. Arnould comments how

And, comments Pantin, "he lets us know that his sensuality did not stop short at smelling scarlet cloth". He was overly fond of music and dancing he says, and indeed he is known to have employed his own troupe of minstrels and had a private dancing chamber built in Leicester Castle. He was, says Grosmont, equally guilty of the sin of lust, and admits—bitterly—to a passion for women, and especially for the "lecherous kisses" of ordinary women–"or worse, whom he liked all the more because, unlike good women, they would not think the worse of him for his conduct". He admits to having taken advantage of his superior social position by extorting money from his tenants, and those "who need it most".

Grosmont then describes the wounds in his soul as having been attacked: the seven deadly sins through his five senses, praying, each time, for a remedy appropriate to the sin. But Grosmont's body is particularly porous: it gushes blood and tears, and wounds are not limited to seven, rather "all the body is so full of wounds." In this way, suggests Arnould, each of his temporal, real-life experiences is given a spiritual equivalent. For example, as a patient of Christ, Grosmont describes how he obtains a theriac of treacle, which he states is "made of poison so that it can destroy other poisons". When the treacle has done its work, the last necessity is a drink of "that rare and precious beverage, the milk of the Virgin Mary".

Metaphors and similes