In 16 weeks, Craig Davidson, a Canadian novelist, transformed himself into a hard-as-nails hunk by injecting illegal steroids. He loved his new body - but not the hideous side-effects. In this graphic account of being a 'roider', he recounts his hellish journey

The needle is 21 gauge, 1.5in. A hogsticker. Forty of them arrived in a package from Greece. Ever received a package from overseas? You get that puff of air when you rip it open - air that's travelled thousands of miles. Foreign, like stepping into a stranger's house. The syringe wrapper has instructions in Italian, French, Greek and Arabic - not a word of English. But it's a needle. Operation is self-explanatory. I had put them out on my work desk a few days ago - an unignorable fact. An invitation. A threat.

Buck up, laddie. Fortune favours the brave.

What's inside looks like oily urine. 1cc of Equipoise - a veterinary drug normally injected into beef cattle - and 2cc of Testosterone Cypionate: 10 times the testosterone a man my size produces naturally in a week.

It was going into my backside; plenty of meat there. But the sciatic nerve radiates from my hips; plus, if I hit a vein I could go into cardiac collapse. I tucked a bag of frozen corn beneath my underwear to numb the injection site. The hash marks on the syringe were smudged away by my sweaty hands. That couldn't be a sign of quality medical equipment, could it?

What if I died in this shitty apartment in Iowa City? I pictured the landlord stumbling upon my body, rotten and bloated. The newspaper headline: Dumbshit Canadian Found Dead with Needle in Ass.

The needle slid in so easily I wasn't aware it'd broken the skin. I aspirated and injected into the deep tissue. When I pulled it out a pressurised stream of blood spurted halfway across the room.

A while ago I wrote a novel. A lot of first-time novelists don't stray far from home: their stories are drawn from their lives. This holds true for me: the main character is... well, me. That's not quite true: he's wealthier, pampered, more intolerant and dismissive. But his deep-seated fears, his inborn weaknesses - those things we share intimately.

My character goes down dark roads. For the sake of the book, I thought I'd travel those roads with him. He begins to work out obsessively. I began to work out obsessively. He joins a boxing club. I joined a boxing club. He takes steroids. I took steroids.

The thing is, I've never done drugs, so I lacked the ability to spot the dealer in a room. Such was my quandary when it came to steroids. Where to buy? Who to ask? I'd heard your local gym was a good place, but I didn't have a clue how to go about that. So I typed 'steroids' into Google, which promptly introduced me to an internet scam. I bought a bottle of what I thought was a steroid called Dianabol. But what I received was Dianobol, which, for all I know, were rat turds pressed into pill form. I won't go into detail about how I came to possess real steroids - or 'gear', as we 'roiders call them. The whole thing makes me look as stupid as I was. Suffice to say, the process involved an encrypted email account, a money order wired to Tel Aviv, and weeks of apprehension (had I been ripped off? Would agents from the Drug Enforcement Administration break down my door?) before a package arrived - pill and ampules and six vials wrapped in X-ray-proof paper.

Anabolic steroids hit US gyms in the early Sixties, courtesy of Dr John Ziegler, the American team doctor at the 1954 World Weightlifting Championships in Austria. He watched in horror as his athletes were decimated by a legion of hulking Soviet he-men who, he later found out, received testosterone injections as part of their training regime. Ziegler teamed up with a pharmaceutical firm to create the synthetic testosterone Methandrostenolone, better known by its trade name, Dianabol.

The biological function of anabolic (tissue building) steroids like Dianabol is to stimulate protein synthesis - that is, to heal muscles more quickly and effectively. New muscle is gained by tearing the long, tube-like fibres that run the length of our muscle; protein molecules attach to the broken chains, creating new muscle. While on steroids, your muscle fibres become greedy, seeking out every stray protein molecule.

At first nobody was willing to credit Ziegler's creation for the amazing gains glimpsed in the first test subjects. Nobody - not least the weightlifters themselves - could get their heads around the idea that a tiny pink pill could be responsible for their newfound strength: lifters added 30lb to their bench press and 50 to their hack squats virtually overnight. These lifters had been taking vitamins for years; they knew the value of pills was minimal. The only thing that convinced them was when Ziegler cut off the supply: the lifters surrendered all their gains and lost the feeling of euphoria experienced while on the programme.

As the Sixties progressed and the results became known, steroids made their way from the hardcore weightlifting gyms of North America into mainstream society, trickling down into baseball clubhouses, Olympic training facilities, and health clubs. Though Dianabol is still perhaps the most popular, today's users can choose from over 40 steroids in the form of pills, patches, creams, and injectable compounds from A (Anavar) to W (Winstrol). Illegal unless prescribed, it is still estimated that one in every 100 people in North America have experimented with steroids at some point in their lives.

I had a misconception that being 'on steroids' involved the ingestion or injection of a single substance, but that was quickly dispelled. Many steroids on their own are either singular of purpose or not terribly effective. This is where 'stacking' comes in: you can put on mass (75mg of testosterone), promote muscle hardness (50mg of Winstrol) and keep water retention to a minimum (50mg of Equipoise). This stack is injection-intensive: Testosterone and Equipoise twice weekly, Winstrol daily. Eleven injections a week.

But that's only steroids - you need other drugs to stave off the potential side-effects, which include: hair loss, gynecomastia (build-up of breast tissue due to increased oestrogen, aka gyno; aka bitch tits), testicular atrophy, cranial and prostate swelling, erratic sex drive, liver impairment, haemorrhoids, impotence, cysts, acne, abscesses, renal failure. Hair loss, gyno and testicular atrophy should be considered absolute rather than potential hazards: you simply cannot expect to alter your body's chemical make-up without your body reacting.

My own steroid cycle went as follows: Dianabol (10mg tabs, 3 per day for the first 4 weeks); Testosterone Cypionate (500mg per week, 10 weeks); Equipoise (400mg per week, 10 weeks); Nolvadex (anti-oestrogen drug; 1 to 4 pills daily, depending on week); Proviron (male menopause drug, 25mg daily); HCG (Human Chorionic Gonadotropin, which is derived from the urine of pregnant women; used during Post Cycle Therapy to restore natural testosterone levels - 500iu twice weekly, administered with an insulin needle).

Believe it or not, it's a fairly mild cycle. Including diuretics and cutting and hardening agents, professional bodybuilders may have 10-15 substances floating around their system at any given time. Like alcohol or drugs, a body's tolerance builds up over time; top pros need to inject 2,500mg of Testosterone or more, weekly, to receive any effect.

Three days into the cycle, my nipples began to itch: onset of Gynomastia. Dump enough testosterone into your body and your system counters by upping its oestrogen output, which leads to a build-up of breast tissue. After long-term use, it can get so bad that some users require surgical breast reductions. I woke up on the morning of day four and nearly had a heart attack at the sight of myself in the mirror. My nipples were the size of milk bottle tops, stretched smooth as the skin of a balloon. The skin had formed into swollen pouches that looked like the rubberised nipples on a baby's bottle. I appeared to have breasts. Pendulous, malformed breasts.

Or was I just chubby and still out of shape? I didn't know. I gave them a jiggle. I couldn't tell if it was fluid build-up or actual flesh. Could a person grow new flesh overnight? I didn't want tits - it went against the purpose of the exercise. I gobbled twice my daily allotment of anti-oestrogen medication. A week's worth of double Nolvadex doses got the gyno under control. But by then my hair had started falling out.

I have a scalp of unruly, bushman-like red hair. While I've never been keen on the colour and its tendency to coil into ringlets when grown out, there has always been plenty of it. Then one morning I was showering, I looked down at my shampoo-foamed hands, and saw dozens of red strands between my fingers. Soon they were everywhere: on my pillow, between my teeth, falling into the pages of books while I read. I became hyper-aware of the way wind felt through my hair: colder on the top of my skull, where there was less protection. And not just my head: the hairs on my arms and legs, even my testicles, were falling out. Not a single follicle seemed firmly moored to my skin.

Then, one sleepless night (the steroids also triggered insomnia) my testicles shrunk. Testicular atrophy is the most well-known side-effect of steroid abuse. It's an inherent irony: here you are trying to turn yourself into an über-man while part of the most obvious manifestation of your manhood dwindles before your eyes. Female users suffer the opposite reaction: their clitorises become so swollen and hard that, in extreme cases, they resemble a tiny penis.

Basically, you pump so much testosterone into your system that you rob your gonads of purpose, they lie dormant for the duration of your steroid cycle. And while I knew this would happen, the physical sensation was beyond horrible. I felt this rude clenching inside my scrotum, like a pair of tiny hands had grasped the spermatic cords and tightened into fists. It happened that fast - like a door slammed shut. 'No more testosterone!' my gonads cried. 'Closed for business!' I sat up, gasping, clutching my testicles to make sure they were still there. In a few days time they had shrunk to half their normal size: plump ripe grapes.

Another sleepless night, a week later, I felt a ridge on my forehead. Cranial swelling - most often a neanderthal-like ridge forming above the brow - is commonly associated with the steroid HGH, or Human Growth Hormone, originally made from the crushed pituitary glands of fresh cadavers. But cranial swelling assumes many forms: in addition to 'caveman brow', some users find semi-solid lumps forming on their foreheads. Some lumps grow to the size of hard-boiled eggs, at which point they require surgical removal.

The next morning, an inspection in the bathroom: was that a slight swelling across the top of my eyebrows? It seemed impossible - this only happens in extreme cases. My own perceived bulge wasn't altogether solid, sort of mushy, but as I smoothed my fingers across my forehead I had this terrifying sense that my bone structure had been somehow altered.

This was the primary fear I ran up against: were these changes happening, and would they subside once I quit 'roiding, or were they permanent? I could handle rampant hair loss, a caveman head, shrunken testicles, hell, even tits - so long as it was temporary. But what if it wasn't?

My sixth injection goes badly. I've been shooting my gluteus and while it's relatively painless the skin has gone tight and I'm thinking the oil hasn't quite dissolved. I elect to stick it in my thigh instead.

I get the needle in three-quarters of an inch before I hit a major nerve. My leg bucks uncontrollably, knee nearly striking my forehead. It takes a few minutes for the pain to subside. Blood leaks from the puncture wound down my leg. I decide I'm not a fan of thigh injections. So I try my calf. Sitting cross-legged, ankle propped on knee, I push the needle in. It goes in easy enough but when I aspirate the syringe fills with blood: I've hit a vein. I wipe the needle with rubbing alcohol and try another spot: again, blood. I boot the excess onto a paper towel, plug a fresh needle onto the syringe, and try again: more blood. It is coming out of my thigh and now from a triangle of holes in my calf. What, am I all veins?

I end up back at my glutes. But I soon regret it: I feel a perfect bubble of oil the size of a pearl onion an inch under my skin. When I massage it the bubble wobbles under my fingertips, all of one piece. It's still there come night time: in bed, I roll onto my side and feel it pressed against my hipbone, solid as a ball bearing. Like the princess with a pea, I have a hard time sleeping.

To embark on a steroid cycle is to devote yourself to rituals. Wake up, eat, medicate, work out, eat, work out, eat, medicate, sleep. Repeat daily for 16 weeks.

Eating becomes a ritual. To maximise muscle growth you must eat one gram of protein for each pound of your weight per day. But I pushed my target further, to around 1.5g of protein per pound - or 337.5g daily.

Consider that a great source of natural protein - a can of tuna - has 13g of protein. That means I'd have to eat 25 cans a day. The most I ever managed was 20, forking it straight from the can. Please believe me when I tell you it is sheer lunacy to eat 20 cans of tuna. Eventually I settle on six cans a day, supplemented with five to six protein shakes. I go through four 2.4lb tubs of protein powder a week, 158lb in all. I keep shovelling a limited range of foodstuffs - tuna, bananas, egg whites, boiled chicken breasts - into my mouth with the listless motions of an automaton. Thankfully the Equipoise, developed to increase lean body weight appetite in horses, gives my appetite a much-needed boost.

Injections become a ritual. Run the vials under hot water to warm the oil. Unwrap a fresh syringe. Draw 1cc Equipoise, followed by 1.5cc Testosterone. Tap the syringe to release air bubbles, push the plunger until a tiny bead forms at the pin-tip. Swab the injection site with alcohol and inject s-l-o-o-o-w, massaging so the oil soaks in.

It isn't much different from the way a heroin addict goes about things: mix the drugs, prepare the needle, find a clean injection site. I reached a point where the careful steps and resultant anticipation became as heady as the rush itself. Those last few weeks, I couldn't stop shaking as I prepared the needle.

The workout becomes a ritual. If the gym is a temple of the body, I went from casual worshipper to fanatical zealot. I pushed myself and found I possessed limits beyond all reckoning. But I'd push myself past the limit, too - twice I caught the smell of ozone, saw awful stars flitting before my eyes, and came to sprawled on the gym carpet. I'd lift until my arms hung like dead things from my shoulders. I took post-workout naps in the changing room, spread out on a bench, too exhausted to walk home.

The prostate is an organ I associate with old men. Surgical-gloved fingers. Not, in any way, an organ I should be aware of. And yet I was, because the benign little organ had swollen to the point where it felt like a fist-sized balloon pressed against my testicles. This is a fairly common side-effect; some professional bodybuilders get prostatitis to such an extent they require a catheter.

I was urinating 15 times a day. A swollen prostate cramps the urethral tube, making it torture to pee. It also presses against the bladder, making it feel as if you always need to pee, even if there's nothing to pass: I stood over the toilet for five minutes, coaxing, cajoling, only to produce a squirt. My urine took on a disturbingly rich hue, like cask-aged brandy.

I heard that 'vigorous manual relief' helped ease prostate pain. But when I tried this, it felt as though the pipe connecting the sperm factory to its exit had been clothes-pegged: nothing much comes out, and the little that does looks embarrassed to be there.

The key was continual application. I became obsessed with manual relief. Four times a day I was manually relieving myself. All that testosterone in my system, it didn't take much to get the motor humming. I was relieving myself to photos of muscle-bound woman gracing tubs of protein powder. I even relieved myself to a perfume sample in a magazine; I relieved myself to a smell - vigorously so!

Wake up, eat, jerk off, work out, eat, jerk off, eat, work out, eat, jerk off, eat, sleep.

The question most sane readers will be asking by this point is: why didn't he stop? Why, despite all the awful side-effects, did he keep plugging needles into himself?

I'm sure my answer is no different to that given by most steroid users: the results.

Once we pass that period of massive physical change - childhood through our teens, puberty and growth spurts - we settle into a sense of our bodies. We understand the parameters and capabilities, what it can and cannot do. And though it's disheartening to say, at 30, I was already finding evidence of a body on its downslope. While I worked out regularly, I hadn't made a sizeable gain in years. In gym parlance, I'd 'hit the plateau'.

Steroids shattered the limitations of my body. I first sensed their effects while bench-pressing dumbbells. I usually peak at 85lb each, or 170lb total. But after 10 repetitions with the 85s I was stunned: it felt like a warm-up! With a degree of trepidation - we're talking weights that, if mishandled, could break a wrist or some ribs - I picked up the 90-pounders, which I'd never attempted. They went up easily and I ripped out 10 reps. It was an out-of-body sensation: somebody else's arms were pushing those weights, someone else's pectorals flexing and contracting.

I went up to 100lb dumbbells - benching roughly my own body weight. I'd been locked at 160-170lb for two years and now, in the course of a single workout, I'd shot up 30lb.

My workout weights rocketed across the board. I was doing wide-grip chin-ups with a 35lb plate strapped to my waist; shoulder-pressing 75lb dumbbells; slapping 45lb plates on the biceps bar to curl 115lb. I was bottoming out Nautilus machines, lifting their maximum weights. My body exploded, 205lb to 235lb in the space of a few weeks - in 'roider vernacular I'd 'swallowed the air hose'.

I became a huffer, a puffer, a grunter, a screamer. Anyone who frequents gyms has seen those guys who make ungodly noises while throwing huge masses of weight around. I'd always found these displays childish and tended to look away, as I would from a toddler having a tantrum in a supermarket. So imagine my surprise to find myself bellowing, shrieking and groaning. It was like a silverback gorilla's mating ritual: I wanted to be seen lifting, wanted everyone to know I was the biggest, toughest motherfucker in the gym. 'Hoooo-aaahhh!' 'Eeeeeee-yahhh!' Look at me! I'm a big boy!

It was pathetic and I should have known better - actually I did know better, but I didn't let that stop me. The 'pumps' I'd get after a workout clouded all judgment. My glances at the gym mirrors were at first baffled: 'Is that me?' double-takes that soon mutated into looks of preening narcissism. I noticed how light played differently upon my chest and arms, the pockets of blue shadow filling my new contours.

The thing is, I knew it was all fake. I hadn't earned it; it was actually quite freakish. But it's like a woman with giant fake breasts: everyone knows they're fake, but damn it if they don't still draw attention.

That oil I shot into my hip weeks ago had not dissolved. The deep pain convinced me I'd developed an abscess. In effect, I've got a pouch of month-old oil inside my hip, walled off by my immune system. If I'm lucky it's sterile, but if not it is infected, the surrounding tissue gone necrotic.

I decide to drain it myself by injecting an empty needle and drawing out the stale oil. My hope is it's still liquid; if it's congealed and lard-like, I'll need medical attention.

The needle sunk into the pocket of infected tissue. The pain was expected and surprisingly bearable. I drew back the plunger and got only a few drops of clear broth. I disconnected the syringe and left the needle jutting out, applying pressure to the surrounding skin. Blood so dark it was almost black dripped down my thigh. Disgusting and more than a little scary, but the pressure subsided. When I'd squeezed as much out as I could, I filled another syringe with sterile water, attached it to the needle still stuck in my skin, injected it, then unclipped the syringe and squeezed most of the water out.

I figured it was a decent job for an untrained meatball like myself. And it did the trick: a week later I was sleeping on my side again.

Week 12, I peak at 240lb. I've packed on 35lb in less than four months. My body has gone through an extreme thickening process. My pectoral muscles are solid slabs of meat hung off my clavicles. My latissimus dorsi muscles flare out from the midpoint of my back: what bodybuilders call a 'cobra's hood'. My triceps and biceps have swollen so much my T-shirt sleeves bunch up at my shoulders, too narrow to fit over my arms.

But the list of physical ailments is mounting. Chronic back pain has set in. I can't walk more than a few blocks before what feels like a fist-sized stone settles upon my lower back. My flexibility has vanished. There are areas I can not reach due to my new size; if I want to scratch my neck I have to go to the cutlery drawer for a fork.

One night I was watching a legal drama on TV - one of those 'ripped from the headlines' type shows. A morbidly obese man was suing a snack company, whom he held responsible for his obesity. It was revealed that the main ingredient in the snack was high fructose corn syrup, a compound that inhibited the hormone leptin, whose function is to send a signal to the brain that the stomach is full - essentially, leptin tells us when to stop eating. But if this signal is never received, a person will go on eating past the point of reason.

Steroids are like high fructose corn syrup. Essentially, they fool a body into a sense that it is stronger and more resilient than it truly is. You accomplish feats that, in your heart and mind, you know are beyond your capacities - and yet you feel so good, so strong, that you convince yourself otherwise. But afterwards it is impossible to deny the toll these exertions have taken on you. After a workout my joints felt like they were hyper-extended. They popped and cracked, noises like wheel nuts rattling in a cement mixer. I felt calcified, hardened, and frighteningly old.

My cycle ends. I've swallowed every anti-oestrogen pill, injected every cc of Testosterone, Equipoise and HGC. By my best estimate, I've eaten 560 cans of tuna, over $750 worth. $1,280 on protein powder. The steroids themselves cost $600.

One morning I wake up and everything has changed. The first thing I notice upon waking is that I feel... well, good. No sluggishness, only minor joint pain. Genuinely refreshed. Then, on my way to the bathroom, I sense a new weight between my legs - my testicles! Fellas, where have you been? Great to have you back, boyos!

The feeling of elation lasts exactly 10 paces: the distance from my bed to the bathroom mirror. I'm staring at a human boneyard. Where are my pecs? I see two shrivelled bags hanging off my chest. My arms - dear lord, my arms! Shapeless shoestrings dangling from a pair of rotten-apple shoulders. My stomach looks like a deflated clown balloon. My legs belong to a coma victim. I step on the scale: 222lb! I've shed 13lb overnight.

Now I realise only the most deluded of 222lb men can stare into a mirror and see a skeletal horror staring back. But I'd become so used to my new body that I felt like a scarecrow with a tear in its belly, bleeding its stuffing all over a farmer's field. The fact that I'd packed on 12lb of raw muscle over four months, that my testicles were up and running again, that I'd woken up feeling better than I had in months - all of this was erased by what I'd lost.

It got worse once I hit the gym. Chest day, which meant dumbbell bench presses. I didn't even attempt to pick up the 105-pounders, which I'd been maxing out with. I settled on the 90s; if I could lift them, it'd be a 20lb increase over my pre-cycle max.

I could barely get the things off my chest. I struggled through a single rep, arms quaking, and halfway through the second the dumbbells crashed down and I rolled awkwardly off the bench, barking my elbows. I felt like a total fraud. Everyone who'd been watching me the past few months as I heaved massive weight about, bellowing like a steer in rut - all these knowing eyes now saw me as a charlatan.

I'd lost it. Everything I'd gained had been washed away. Popeye without his spinach. Weak and broken and utterly human. All the needles, the gallons of protein I'd chugged, pound after pound of tuna, the urine of pregnant women running through my veins, the fainting spells and sleepless nights, the muscle knots and bitch tits and shrunken gonads and the hair in my food and abscesses and caveman brow - every risk I'd taken, all that sweat and toil for nothing.

I fell into a week-long funk. I cleaned my apartment out: the unopened cans of tuna, the uneaten protein powder - all of it went in the bin. I ordered a large pizza, pepperoni and double cheese. I wolfed it down with gulps of Pepsi. I wanted to get fat and disgusting. I wanted to inflict damage upon myself. The rational part of my mind was going, 'You did the research - you knew this was bound to happen.' But the other part of my mind - the part closer to my body, the part now accustomed to the sly weightroom looks and the more defined, somehow burlier cast of my shadow, the part that relished how people ceded plenty of room as they passed me on the city's narrow pavements - that part of me was not to be consoled.

I headed to the doctor's. Though I felt much better now that it was over, I was still suffering aches and pains. The results: a partially herniated disc in my lower spine, the result of either bad posture or an accumulation of pressure due to excess body weight. A chiropractic visit was scheduled. An enlarged prostate. I was prescribed Avodart, which worked wonders.Fluid build-up on left knee - again, the result of excess weight. The doctor told me he'd get back to me with the blood test results.

I started out weighing 205lb and ended up at 208. My body looks no better now - if anything, it's worse. Bloated somehow, like I'd died, my body abandoned in a gassy swamp. The gyno has left nipple-nubbins that poke out when I wear anything tighter than a golf shirt.

Has it been worth it? The question presupposes that I expected to benefit from the experience. I embarked on the steroid cycle in order to bring a level of real-world verisimilitude to my novel. I wanted to feel what my character felt, experience a portion of his life, write with conviction about what he went through.

In a way, I am ashamed of myself. Was it worth it - all for a book? What have I done to myself in the long run? Jeopardised my chances of having a child, perhaps. I worry about that a lot. More than anything else.

Has it been worth it? Somewhere along the line I'd been let off the hook. My grandfather, father, uncles, men of generations past - they didn't get the free pass I did. Their lives were about poverty, warts, factory floors, untilled fields. They endured. What have I ever had to endure? I felt unworthy of all I'd been so carelessly given. And I loathed myself for taking it.

I currently weigh 170lb. The blood tests showed my liver values were totally out of whack. As I had never been able to convince a woman that I was a viable prospect to make a baby with before, I'll never know if an inability to conceive, should that be the case, is attributable to steroids or the innate decrepitude of my seed.

Did I take steroids to write a book, or did I write a book as an excuse to take steroids? Often, all you want is to step off the path you've carved. And when my body began to fall apart, when the drugs began to destroy me, I persisted in the belief that all suffering on my part was long overdue. I would endure. The eventual understanding that a certain nobility underlay my grandfather's suffering, whereas mine was not much more than a masochistic stubbornness - I'd like to think that stopped me. And when I'd stared at myself, naked and porcine, in the bathroom mirror, I told myself that if nothing else, I had suffered. I'm ashamed to admit, I took pride in that too.

'Mr Davidson,' the doctor asked over the phone, 'are you on any herbal medications or' - a pause - 'bodybuilding supplements?'

'I was on creatine,' I told him, creatine being a legal bodybuilding supplement.

'Mr Davidson.' Another pause, followed by a heavy exhale. 'Never, ever take creatine again.'

The doctor hung up on me.

· The Fighter by Craig Davidson is published by Picador on 6 June. To order a copy for £7.99 with free UK p&p go to observer.co.uk/bookshop or call 0870 836 0885