Ever since the first couple of times I'd smoked it, in my early 20s, I had always maintained a great interest in heroin. I'd sort of fallen in love with the warmth of it - the way it felt like crawling back into the womb. Heroin delivered. LSD does a bit, especially when all the things that are familiar to you peel away and you suddenly realise the fragility of how you normally see the world. Marijuana doesn't really, although it's a laugh for a while (I say that having smoked it constantly for a decade). Alcohol makes you sick and gives you a headache. Crack is like inhaling plastic, but so brief and flimsy and brittle as a high. Normal cocaine just makes you nervous, amphetamines are even worse, and ecstasy never really agreed with me. But heroin gets the job done.

All of us, I think, have a vague idea that we're missing something. Some say that thing is God; that all the longing we feel - be it for a lover, or a football team, or a drug - is merely an inappropriate substitute for the longing we're supposed to feel for God, for oneness, for truth. And what heroin does really successfully is objectify that need.

It makes you feel lovely and warm and cosy. It gives you a great big smacky cuddle, and from then on the idea of need is no longer an abstract thing, but a longing in your belly and a kicking in your legs and a shivering in your arms and sweat on your forehead and a dull pallor on your face. At this point, you're no longer under any misapprehension about what it is that you need: you don't think, "Nice to have a girlfriend, read a poem, or ride a bike," you think, "Fuck, I need heroin."

And I never had much trouble getting it, especially when I was working as a presenter at MTV's Camden studios. Heroin was everywhere in Camden: little blue bags the size of, I suppose, two peas. That's how big a £10 bag is - half the size of a Malteser, twice the size of a pea. Just in case you ever become a junkie and you need to score in north London, you can take this article with you as a guide to weights and measures. "That's not £10 worth, you scumbag. Look at this Malteser." Possibly that'll be the last sentence you utter before being flung into a canal.

The dealers keep the bags in their mouths. When you buy one they spit it into their hand and you have to put it directly into your mouth. Even though you want the heroin, a little bit of you is thinking, "Eeugh! He's had it in his mouth." After a while, though, you stop thinking that. It's a bleak day when that happens. You know that's another little boundary that you've crossed, another principle chalked off to experience, another thing you've put behind you, because there's so little in front of you.

"All my days are empty and the pages of my diary are all silver foil, with nought but an inky black snake carving its way through the days," I once wrote. Probably to impress a girl.

Once I started hanging out with homeless people in the West End, scoring heroin with them, I realised that there's this secret culture of people going up and down Oxford Street, whistling and yelping to each other in a kind of tropical slang - men on BMX bikes delivering £10 bags of heroin to be purchased with grubby fists full of 50p and 10p and 2p coins; West Indian housewife-type women perambulating past Topshop, cheeks wedged with packets of smack.

You don't see this bustling underworld until you need to. There have been occasions, thrilling to me, when I went off to score, cutting a purposeful stride down past Tottenham Court Road tube station in the company of three or four homeless people, their sleeping bags worn about their shoulders, like the cloaks of Roman legionaries. I must have cut a ridiculous figure, dressed in my MTV-presenter attire - skintight white jeans, graffitied tops, Ray-Ban sunglasses - jostling along with them, as they set off in search of a bag in Covent Garden.

Until recently, when I gratefully gave up public transport, I would see people I'd scored drugs with begging in tube stations. There was one bloke - I don't know if he's still around - whose eyes were missing. First he lost his wife, then his house, then his shoes, then his eyes; heroin is a greedy drug, robbing you by increment first of your clothing, then of your skin; when it finally comes for your life it must be a relief.

The first time I realised I'd become addicted to heroin, I was staying with Amanda, the woman I've come closest to loving, in a risible 70s-style hotel in Ibiza. We lived together for six years, on and off, sometimes in Spain, where she came from, and sometimes in Britain, but there was never any prolonged period when we were what you'd call comfortable together. I'd go to see her in Ibiza, and we'd just ricochet from argument, to sex, to argument. (I remember chasing her down the street in nothing but a towel once, shouting, "Please come back!") Then I'd return home to London, to a life of whores and heroin. I wanted Amanda with me always, but because we spent most of our time apart, I went through a lot of psychological tumult, and increasingly used heroin to take the edge off. When things went well, I'd smoke heroin to celebrate, and when they went badly, I'd smoke some to comfort myself. "Mustafa Skagfix", my mate Matt nicknamed me, after I acquired a predilection for wearing Arabian robes.

Amanda didn't like me using heroin. She knew I'd been doing it in London, but I'd told her I'd given up, so I had to hide my drug-taking from her. On this occasion, though, there had been no opportunity for me to smoke it in secret. When I said I thought I might go for a walk, Amanda was suspicious and insisted on coming with me. At that point I began to get anxious. I could feel myself heating up and breaking out in a sweat, and then my legs started kicking and jumping. That's the worst symptom of heroin withdrawal; I can tolerate the nausea and the sweating, but I hate it when your legs go all kicky. That's where the phrase "kicking the habit" comes from.

Amanda eventually fell asleep, and I had to go into the bathroom and quietly unfold all the things I needed, which I'd managed to secrete about the place. I got the foil out, sat on the toilet, lit the lighter under the foil, and the tiny lump of heroin started to liquefy and bubble. Then it begins to run along the foil, and as it does so a vapour escapes, and you have to hover above it, sucking it up with a tube.

I remember being very conscious of the sound of the lighter, then almost as soon as the smoke had hit the back of my throat, that feeling - the kicky leg, the sweating - it just went. It was like turning off a light. Then I could lean back and everything was suddenly all relaxing and beautiful. It was at this point that I knew that I was an addict, though the pain of that realisation was greatly mitigated by the impact of the heroin: that's how it gets you.

I used to get in a lot of trouble going back and forth between London and Ibiza. One time, my pursuit of drugs led me to be shot at with what Matt describes as "a tiny gun". I was on my way to the airport, and I had to go to this estate in Swiss Cottage, taking the dealer with me in the MTV account car.

I had dealings with this individual over a long period of time without ever being sure if he/she was a man or a woman. Anyway, me and the androgynous creature went to the tower block where Goldie used to live (the drum'n'bass pioneer plays no further part in this anecdote - it was just that whenever you had to go anywhere near that place, people always used to point it out and say, "Goldie lived there"). The driver took the dealer's bike out of the back of the car, while he/she went inside to get the drugs, and as he/she did that a pellet pinged off the top of the car. Someone was firing at us from inside the block.

It might seem a bit reckless to be picking up drugs on the way to Heathrow, but my need for a regular supply of narcotics would not be constrained by the exigencies of international air travel. I generally travelled with drugs up my arse in the belief that if customs officers decided to pursue this unsavoury line of inquiry, my day would already be ruined, and the discovery of crack or heroin couldn't make it much worse.

Eventually I succeeded in convincing Amanda to leave Spain and come and live with me in London. Her two conditions for doing this were that 1) I quit heroin, and 2) I get us somewhere to live. In pursuit of the first of these goals, my friend Martino booked the three of us a cottage in the Cotswolds. The last night (as I grandly, though ultimately inaccurately, styled it at the time) of my using, I was presenting the annual awards for some dance music magazine.

I had a coterie of friends around me, including Amanda. I smoked abundant marijuana, smack and crack, and drank a skinful, as well as taking four tabs of Viagra, so I could still fuck. At one point, I mispronounced the name of a famous DJ (I think it was Danny Tenaglia, but I'm not sure even now) and fell off the stage. Boy George wrote in his Daily Express column that I had been brilliant and had done it all deliberately. The canyon between the perception of me and my actual reality seemed to be widening on a daily basis.

The next day, me, Amanda and Martino took an MTV cab to the Cotswolds, costing them £400. I took a bottle of Jack Daniel's, an ounce of weed, and loads of videos to get me through my rattle (as we denizens of the drugs underworld term it). It was awful - hot and cold, nausea, and, worst of all, I remained horrifically awake all weekend. The best thing about heroin is it turns your life into a waking dream, but then, when I needed it most, my mistress sleep had deserted me.

I still made it through, though, with Amanda and Martino's help, and managed to fulfil the other precondition for Amanda moving to London, by renting this ridiculously gorgeous flat, just off Brick Lane. This glamorously empty warehouse-style apartment soon echoed with misery, as our relationship almost instantly became a psychological war.

Amanda was a strong, beautiful woman. After a string of infidelities on my part, she finally had the good sense to leave me. I just came home one night, and all her clothes were gone. I thought this a flabbergasting affront, and threw myself with ever more self-destructive intensity into my work, womanising and, above all, a renewed and increasingly all-encompassing relationship with heroin.

I thought, "Well, at least now she's left me, I can just take loads of drugs again".

Not content with damaging myself physically, I set about dismantling my career. Gritty was the main dealer I used to get heroin off when I worked at MTV. I liked the fact that destiny had allotted him the name "Gritty". Just as Ned Ludd, leader of the Luddites who opposed the Industrial Revolution, would have struggled to make such an eloquent case against the spinning jenny had his name been Fabrizio Zodiac, so the name Gritty seemed well adapted to the needs of his profession.

He seemed a nice sort of man, though. He had quite a caring side to him, for a drug dealer. I remember one occasion when I was buying drugs off him near Camden Bridge. Having just sold me my two £10 bags of smack and two £10 rocks of crack, he gave me a sincere look and said, "Be careful with that, won't you Russell?" I was thinking, "What do you mean, 'Be careful with that'? They're drugs. What does he think I'm gonna do with them? 'Oh no, I seem to have taken them. Why didn't I heed Gritty's prophecy?' "

One day Gritty asked me once if he could bring Edwin, his eight-year-old son, into MTV to have a bit of a look round. I said, "Sure, why not?" What could possibly go wrong? We could call it Bring Your Drug Dealer to Work Day.

The date that the inaugural BYDDTWD happened to fall upon was September 12 2001, the day after the destruction of the World Trade Centre. With typical restraint, I decided to go into work dressed in a camouflage flak jacket, a false beard and a tea towel on my head, held in place by a shoelace.

I had been aware of Osama bin Laden for about a year. He wasn't someone people of my age group generally knew about, but he'd been involved with some other bombings and he was top of the FBI's most wanted list, and I was fascinated by that sort of stuff. That day, I was going to present this programme called Select, where kids phoned in and chose videos for us to play, and pop stars would come on to flog their records. Our guest was to be Kylie Minogue. Me, Gritty and Edwin went into the toilet and the two older members of our party smoked some crack. Edwin didn't have any. He was just a little boy, and seemed quite upbeat about life anyway. Children don't need drugs, because they have sweets.

We blearily swaggered out of the disabled toilet. On the other side of the foyer - with its round console, banks of TVs, trendy turnstile and endless parade of beautiful young people of both genders and every sexual persuasion trundling in and out - I saw Kylie Minogue, all famous and everything.

Somewhere in my mind, the artist within me - the situationist within me - thought: "I can create a moment here. When am I ever going to get an opportunity like this again?" Before I knew it, I'd walked across that foyer, made a kind of "Woo-ooh" noise - in a mum-across-a-neighbour's-fence sort of way - and said: "Kylie, meet Gritty." Then I just stood back to watch it unfold.

What were these two going to talk about? It's the day after 9/11, and Kylie and Gritty are having a sort of awkward chat, with Gritty trying to be polite and Kylie asking, "What do you do?" sort of like the Queen would. And there's me standing beside them, still dressed as Osama bin Laden.

I thought: "It don't get any better than this."

And it didn't, cos they sacked me about two days later.

· My Booky Wook, by Russell Brand, is published by Hodder & Stoughton on Thursday, price £18.99. To order a copy for £16.99 with free UK p&p go to theguardian.com/bookshop or call 0870 836 0875.