The idea that literature can make us emotionally and physically stronger goes back to Plato. But now book groups are proving that Shakespeare can be as beneficial as self-help guides. Blake Morrison investigates the rise of bibliotherapy

At a reading group in Birkenhead, nine women and two men are looking at Act 1 scene 2 of The Winter's Tale, in which Leontes and his wife Hermione urge their guest, Polixenes, not to rush off back to Bohemia. Some of the language is difficult to grasp: what's meant by "He's beat from his best ward"? or "We'll thwack him hence with distaffs"? But thanks to the promptings of the group leader, Jane Davis (from the Reader Centre at the University of Liverpool), Shakespeare's meanings are slowly unlocked, and discussion ranges widely over the various issues the passage raises: jealous men, flirtatious women, royal decorum and what to do with guests who outstay their welcome.

The rise of book groups is one of the most heartening phenomena of our time, but this is an unusual one, including as it does Val and Chris from a homeless hostel, Stephen who suffers from agoraphobia and panic attacks and hasn't worked for 15 years, Brenda who's bipolar, Jean who's recovering from the death of her husband, and Louise who has Asperger's syndrome. Most of the group are avid readers but for one or two it's their first experience of Shakespeare since school.

Under the umbrella of Jane Davis's "Get into Reading" scheme, there are now around 50 groups like this across Merseyside: groups in care homes, day centres, neurological rehab units, acute psychiatric wards, cottage hospitals, sheltered accommodation and libraries; groups for people with learning disabilities, Alzheimers, motor-neurone disease, mental health problems; groups for prisoners, excluded teenagers, looked-after children, recovering drug-addicts, nurses and carers; groups that are small - no more than 10 - so there's a sense of intimacy.

The educational backgrounds vary widely but there's no dumbing down in the choice of texts - The Mayor of Casterbridge, Uncle Tom's Cabin, Rebecca, Great Expectations, Adam Bede, Jane Eyre, Of Mice and Men, Kes, even Robert Pirsig's The Art of Motorcycle Maintenance among them. The usual pattern is for a complete book to be read aloud, cover to cover, at weekly sessions, which for a group spending an hour a week on a Dickens novel can mean six months devoted to a single work. Nobody is pressured to read aloud, but if and when they do the boost to their confidence can be striking.

These reading groups aren't just about helping people feel less isolated or building their self-esteem. Nor are they merely a pretext, in an area of high unemployment, for giving the experience of working as a unit. More ambitiously, they're an experiment in healing, or, to put it less grandiosely, an attempt to see whether reading can alleviate pain or mental distress. For Kate, who has suffered from severe rheumatoid arthritis for 30 years, the answer is clear: "Reading pushes the pain away into a place where it no longer seems important. No matter how ill you are, there's a world inside books which you can enter and explore, and where you focus on something other than your own problems. You get to talk about things that people usually skate over, like ageing or death, and that kind of conversation - with everyone chipping in, so you feel part of something - can be enormously helpful." Others say the same: "I've stopped seeing the doctor since I came here and cut down on my medication"; "being in a group with other women who have what I had, breast cancer, didn't help me, but talking about books has made a huge difference."

Medical staff tell stories of the remarkable successes they've seen: the neurological patient who sat in a group saying nothing for months, then after a reading of George Herbert's poem "The Flower" ("Who would have thought my shrivelled heart/Could have recovered greenness?") launched into a 10-minute monologue at the end of which he announced "I feel great"; the brain-damaged young man whose vocabulary significantly increased after he joined a book group; the husband caring for his disabled wife whose exposure to poetry has proved not just a respite but a liberation. To outsiders, the outcomes might seem small, but to the staff and patients concerned they're huge breakthroughs.

Crochet or bridge might serve equally well if it were merely a matter of being in a group. But as Judith Mawer of the Mersey Care Mental Health Trust explained, focusing on a book is the decisive factor: "People who don't respond to conventional therapy, or don't have access to it, can externalise their feelings by engaging with a fictional character, or be stimulated by the rhythms of poetry."

One particularly successful initiative has been reading poetry to and with dementia patients, some of whom have lost all sense of who and where they are but can recite the words of a poem learned at school 70 years ago. As Get into Reading worker Katie Peters describes it: "One lady was shouting and swearing at anyone who approached, and when I mentioned poetry told me in no uncertain terms to go away. But as I sat and read poem after poem, she visibly relaxed, her mood changed completely and she happily chatted about the poems to other residents.

"Nurses tell me that patients seem less agitated after our sessions. There is something about poetry, not just the rhythms and rhyme but the way it provides an opportunity to hold a thought together through time, that really helps, even with people who are not natural readers." Katie's experiences echo those of Oliver Sacks with patients suffering from severe Parkinson's disease, who found that "people who could not take a step could dance" and "people who couldn't utter a syllable could sing".

"One sheds one's sicknesses in books," DH Lawrence once wrote, and the people I met on Merseyside agree with him that books - good books, anyway - are a form of therapy. "Prose not Prozac" is the prescription. Literature not lithium. A talking cure in the presence of Keats, Dickens or Shakespeare rather than a physician or psychiatrist.

Bibliotherapy, as it's called, is a fast-growing profession. A recent survey suggests that "over half of English library authorities are operating some form of bibliotherapy intervention, based on the books-on-prescription model". That's to say, an increasing number of people are being referred by their GPs to the local library, where they'll find shelves or "reading pharmacies" set aside for literature deemed relevant to their condition. Lapidus, an organisation established in 1996 "to promote the use of literary arts in personal development", has played a key role in bringing together writers and health professionals; as has the current editor of the Poetry Society's magazine, the poet Fiona Sampson.

Bibliotherapy might be a brave new word but the idea that books can make us better has been around for a very long time. Matthew Arnold and FR Leavis temporarily hijacked it when they argued that great literature - "the best that has been thought and said in all the world" - can make us morally better, by kindling "our own best self". That idea disappeared with the Holocaust, when immensely civilised and well-read men brought up on Schiller and Goethe proved capable of the most barbarous acts. But the idea that books can make us emotionally, psychologically and even physically better goes back to the ancient world.

Plato said that the muses gave us the arts not for "mindless pleasure" but "as an aid to bringing our soul-circuit, when it has got out of tune, into order and harmony with itself". It's no coincidence that Apollo is the god of both poetry and healing; nor that hospitals or health sanctuaries in ancient Greece were invariably situated next to theatres, most famously at Epidaurus, where dramatic performances were considered part of the cure. When Odysseus is wounded by a boar, his companions use incantations to stop the bleeding. And the Bible has the story of David calming Saul: "And it came to pass, when the evil spirit from God was upon Saul, David took a harp, and played with his hand: so Saul was refreshed, and was well, and the evil spirit departed from him."

By the Renaissance, the idea that poetry and song could "banish vexations of soul and body" was well-entrenched - to the point where Thomas Puttenham argued, in The Art of English Poesie, that the poet must "play also the physician and not only by applying a medicine to the ordinary sickness of mankind, but by making the very grief itself (in part) cure of the disease". What Puttenham meant was that the writer should use "one dolour to expel another", the sad cadence in a line of poetry allaying the burden of pain or depression in the reader, "one short sorrowing a remedy of a long and grievous sorrow".

The image has a hint of homeopathy about it - like curing like - and just as homeopathy is regarded with suspicion in conventional medicine, so bibliotherapy is bound to strike sceptics as a form of quack medicine. But considerable research has been carried out over the past 20 years which seeks to prove the healing capacity of the arts in general and literature in particular. A study in Alabama demonstrated how depressives treated via bibliotherapy had less chance of relapse than those given medication. At Kings College, London, Gillie Bolton has explored the use of writing with a range of palliative care patients and teenage cancer sufferers. Other studies have explored the links between involvement in the arts and longevity; between "verbally revealing it all" and fighting off infections; between the generally calming effect of books - relatively few of which are so bad that we want to hurl them across the room and - and lower levels of cardio- vascular disease. An Arts Council report of 2004 cited 385 references from medical research on the positive effect of the arts and humanities in healthcare, among them "inducing positive physiological and psychological changes in clinical outcomes, reducing drug consumption, shortening length of stay in hospital ... and developing health practitioners' empathy".

The scientific evidence is far from conclusive, nevertheless. Raymond Tallis, author and emeritus professor of geriatric medicine at University of Manchester, has been enormously impressed by Jane Davis's work, but notes that most of the published research "consists of equivocal findings in fourth-rank journals", adding: "I have been a medic too long to be easily persuaded of the wider role of literature in healing. No one sends out for a poet when they are seriously ill." However, even he concedes that "my last boss before I became a consultant was hugely helped in his last weeks by reading War and Peace, when he was attached to a diamorphine pump." Tallis also acknowledges that reading might be therapeutic in a variety of ways, not least in easing depression: "the pleasure of escape into a parallel world; the sense of control one has as a reader; and the ability to distance one's self from one's own circumstances by seeing them from without, suffered by someone else and gathered up into a nicely worked-out plot - somewhere around here is the notion of the Aristotelian purgation and Sartre's idea of 'the purifying reflection'."

Perhaps the most convincing argument for the effectiveness of bibliotherapy comes from writers themselves. There's the case of George Eliot, for example, who recovered from the grief of losing her husband George Henry Lewes by reading Dante with a young friend, John Cross, who subsequently married her. "Her sympathetic delight in stimulating my newly awakened enthusiasm for Dante did something to distract her mind from sorrowful memories," Cross later wrote. "The divine poet took us to a new world. It was a renovation of life."

John Stuart Mill enjoyed a similar renovation after the "crisis in my mental history" which he describes in his Autobiography, a crisis that began in the autumn of 1826 when "the whole foundation on which my life was constructed fell down [and] I seemed to have nothing left to live for". Then one day "a small ray of light broke in upon my gloom. I was reading, accidentally, Marmontel's Mémoires, and came to the passage which relates his father's death ... A vivid conception of the scene and its feelings came over me, and I was moved to tears. From this moment my being grew lighter. The oppression of the thought that all feeling was dead within me was gone. I was no longer hopeless: I was not a stock or a stone."

What cured Mill was an account of death; what eased Eliot's mourning of her husband was a journey through Dante's Inferno. If books are to be therapeutic, it seems, it's because they take us to dark places rather than bright ones. As Thomas Hardy recognised, "If a way to the better there be it exacts a full look at the worst." Hence Davis's preference for classic texts which address existential concerns, not anodyne pep-ups. Medical staff attached to her scheme have occasionally worried that such and such a poem or passage might "make things worse". But what does "worse" mean when you're talking about people on a psychiatric ward? One elderly patient became distressed during a reading of Burns's "My love is like a red, red rose", but insisted on staying there, through the tears, and professed herself "much better for it" afterwards.

Hardy's famous quote comes from a sequence of three poems, "In Tenebris", which he wrote in 1896-97, when his spirits were brought low by the excessive optimism of his peers. To Hardy, hell was other people being cheery - "the blot seems straightway in me alone .../one born out of due time, who has no calling here". And yet he derives consolation from the very pessimism or "unhope" that weighs him down:

Wintertime nighs;

But my bereavement-pain

It cannot bring again:

Twice no one dies.

Each of Hardy's "In Tenebris" poems has an epigraph from the Psalms. And far from being a simple glorification of God, the Psalms are often engulfed by despair: "my heart is smitten, and withered like grass"; "attend unto my cry; for I am brought very low". Yet reading the Psalms or Hardy or Gerard Manley Hopkins's "terrible sonnets" can be cathartic. By attending to the cry of another, we articulate our own cries, frame them, contain them, and feel less stranded. "I wake and feel the fell of dark, not day," Hopkins writes, in his anguish:

What hours, O what black hours we have spent

This night! What sights you, heart, saw, ways you went!

And more must in yet longer light's delay ...

Though Hopkins plumbs the depths, he writes so searingly of his torment that the poetry becomes a cauterising iron to burn away his pain and ours, and to "leave comfort root-room" in which to grow.

Hopkins knew that not everyone will have experienced the "cliffs of fall,/Frightful, sheer, no-man-fathomed" which he describes: "Hold them cheap/May who ne'er hung there". But even those of a sunny disposition will find his sonnets illuminating, an insight into the mind of a fellow creature, and an expansion of their own empathic powers.

This is surely the other great therapeutic power of literature - it doesn't just echo our own experience, recognise, vindicate and validate it - it takes us places we hadn't imagined but which, once seen, we never forget. When literature is working - the right words in the right place - it offers an orderliness which can shore up readers against the disorder, or lack of control, that afflicts them. Most misery memoirs fail in this respect - they invite readers to be prurient rather than to identify, exaggerate where no exaggeration is necessary, and are too clamorous to grant the space to contemplate and withdraw.

In The Prelude Wordsworth speaks of certain memories or "spots of time" - "scattered everywhere" - which have a special place in the life of each man and woman, and which it is our task to recover: not as an act of nostalgia but because they help repair and (the word John Cross used) renovate us if we find them.

There are in our existence spots of time

That with a distinct pre-eminence retain

A renovating virtue, when, depressed

By false opinions and contentious thought,

Or aught of heavier and more deadly weight,

In trivial occupations, and the round

Of ordinary intercourse, our minds

Are nourished and invisibly repaired;

A virtue by which pleasure is enhanced,

That penetrates, enables us to mount,

When high, more high, and lifts us up when fallen ...

The most consciously renovating or therapeutic writer I know is Ted Hughes - surprisingly, perhaps, since in his lifetime he seemed to friends, and accused himself of being, a man in denial. But he not only considered individual works of his medicinal - "It is a story intended to cure the mentally sick," he said of his children's book The Iron Man - but defined poetry as "nothing more than a facility for expressing that complicated process in which we locate, and attempt to heal, affliction - whether our own or that of others whose feeling we can share. The inmost spirit of poetry, in other words, is at bottom, in every recorded case, the voice of pain - and the physical body, so to speak, of poetry, is the treatment by which the poet tries to reconcile that pain with the world."

When Hughes describes poetry as consisting of "things we don't actually want to say" but "desperately need to share", he is talking as a writer, not a reader. But the inseparability of reading and writing is something which Proust acknowledges when he defines the book as a "sort of optical instrument which the writer offers to the reader to enable the latter to discover in himself what he would not have found but for the aid of the book". It's often said that books "take us out of ourselves", but in reality the best literature is surreptitiously taking us inside ourselves, deeper than we might have expected or chosen to go.

The self can get help from a book, then. But the best kind of help doesn't necessarily come by way of self-help books. Nor are the books which make us feel good usually feelgood books. That's the problem with most of the bibliotherapy schemes that have been set up in the UK so far. It's commendable that Kirklees, Calderdale, Neath and Ayrshire - to name just four such initiatives - should have thrown their weight behind bibliotherapy. But too often the prescribed "literature" in local libraries consists only of leaflets, or references to useful websites, or books written by "eminent therapists or former service-users" which are worthy, practical-minded and dull. There's no recognition that people in trouble need more than the right labels. As one of the reading group in Birkenhead explained: "I would never have gone into a library and asked for a self-help book on depression. I was feeling bad enough as it was, and that would have made me feel worse. It's being in a group and talking that helps." And, of course, using imaginative literature - poetry and fiction, not self-medicating pamphlets.

Jane Davis would like the scheme she's created on a Merseyside to be adopted throughout the country. With 2008 designated the Year of Reading, and Liverpool the 2008 European Capital of Culture, it's an opportune moment. If she's evangelical in the cause (she also runs the excellent quarterly magazine the Reader), that's because of the almost religious role which books have played in her own life - notably, Doris Lessing's novel Shikasta, reading which, as a young woman, pushed her "into something like a nervous breakdown. I felt so disturbed by it that I wrote to Doris, care of her publisher, blaming her and asking for help. She wrote back telling me to read more and offering money for books if I needed it. 'I am not your teacher but you need to read,' she said. I was a single mother living on social security but in the end I decided what I needed wasn't Doris's money but a public library. And, for me, the clue of Shikasta - that life is serious and you have to do something with it - was a life-saver."

Books don't always save lives: writing about the Holocaust didn't prevent Primo Levi from ultimately committing suicide; and the reading - or perverse misreading - of The Satanic Verses led to the deaths of innocent people. But literature's power to heal and console outweighs its power to do damage. Hector, in Alan Bennett's The History Boys, puts it beautifully when he describes how, in the presence of great literature, it's as if a hand has reached out and taken our own. That's the hand which Davis is trying to extend.

· www.getintoreading.org, www.thereader.co.uk

· This article was amended on Friday January 11 2008. Fiona Sampson was mistakenly described as chair of the Poetry Society. She is editor of the society's magazine, Poetry Review, and the chair is Anne-Marie Fyfe. This has been corrected.