I recently collected a further two months' supply of Efexor XL, an antidepressant that has become as much a part of my daily life as toothpaste or water. Twice a day, with breakfast and dinner, I pop a pink pill, a magic composite of depression and anxiety relief. An hour or so after popping each pill, my veins are woozy with a devil-may-care cartoonish bravery.

If my whole life were an expansion of that moment when the drug hits my bloodstream, then I would probably end up doing all sorts of reckless things, such as climbing K2 or heading off to Florida for a spot of alligator wrestling. The problem with pills is that they rewire you. At this point, aged 33, I have taken so many pills and potions that I honestly wouldn't know my natural state if it came up to me in the street and clubbed me over the head.

But despite this, I keep taking the pills because if I don't, I start wanting to do really reckless things such as cutting or burning myself. Or climbing up on to a bridge and taking a flying leap. So I exist in a Catch-22 situation: take the pills or self-destruct.

When I was younger, I kept voting to self-destruct. I took drugs - the kind you buy in a shady club in Deptford, not the kind they give you in Boots - and I drank. When I was 24, I wound up in hospital with a bleeding stomach and a whole litany of other self-inflicted ailments, and I knew that I was an alcoholic.

The day I left hospital to embark on what has been nine years of difficult but rewarding sobriety, I started voting for pills. Pills to calm me down. Pills to help me sleep. Pills to stop me wanting to kill myself.

It's no wonder that my wife, Anna, upon watching the dire routine of my pill habit, has developed a new nickname for me. Thanks to the gross side-effect of putting on colossal amounts of weight while taking Efexor XL, a drug that alleviates depression but leaves you depressed about your size, she has more than once suggested that I am going through my Elvis at Vegas phase.

I don't disagree. After all, I am caught in a trap. And I can't back out. It's just the way things are. This depression stuff, this anxiety stuff, this recovering alcoholic business, this merry-go-round of pills of all colours, shapes and sizes, is who I am. Or on days when I'm feeling despondent, who I have become. In pills I trust. Has it come to this? Well, frankly, if it's the difference between carrying on a relatively "normal" life or wanting to chuck myself off the nearest cliff, I would rather take the medication.

Last month, I took a giant step. I told my doctor that I wanted to try a lower dose. He reminded me what happened the last time: within a month I was begging for the higher dose, all the symptoms that had led me to the drug in the first place having returned in a flash. Regardless, I told him that I felt ready to give it another go. Shrugging his shoulders and warning me to expect the same withdrawal symptoms, he dropped me from 150mg to 112.5mg. I went home and waited for the shit to hit the fan.

Sure enough, within a week, I was sleepless in south-west London, worrying excessively about everything, feeling panicky and crying over the stupidest little thing. On the plus side, I was losing weight, staying awake after 10 in the evening (previously I turned, Cinderella-style, into a drugged-up pumpkin at 10.01 and passed out) and best of all, I could actually think clearly. On down days, I would freak out, certain that the depression and anxiety were taking over again. But there were also OK days. And on those, I vowed to stick it out this time.

At the next appointment, my doctor gave me two choices: either I could stay on the new dose for a further two months or I could return to 150mg. A part of me wanted to say: "Look doc, I quit. Give me the 150." But I knew that would be a cop-out, so I took another prescription for the lower dose. I still don't know if that was a sensible decision.

But regardless, I still dream of getting off these anti-depressants, in much the same way that my 83-year-old grandfather tells me he spends night after night staring at the armchair once occupied by my recently deceased grandmother, hopeful that if he stares hard enough and waits long enough, she will reappear.

· A Head Full Of Blue by Nick Johnstone is published by Bloomsbury, £6.99.