The life doctor: The greatest substance ever sold

ZING! The zestful invigorating glow that will overwhelm you if you start drinking hot water with squeezed lemon juice first thing in the morning instead of your usual caffeine injection. ZING! the essential opener of any magazine guide to a "new you". The idea that replacing caffeine with something "purer" will give you more energy and inner calm somehow makes perfect sense. Your skin will improve as the toxins are flushed out and you will lose weight because the body, free from the poison, no longer craves other unhealthy substances.

Thus reasoned Carrie Wicks, general manager of the celebrity's favourite Covent Garden Hotel, who gave up caffeine two weeks ago. "I was drinking about three cups of tea and four cups of coffee a day. It felt like too much, I was feeling sluggish. Sometimes, if I'd had too much, the adrenalin would be pumping, I'd feel like my eyes were being pulled out and I'd have palpitations.

"I gave up on the Monday morning. The headaches started on the left hand side of my head on Tuesday afternoon. They were excrutiating - although to be honest they dulled when I had a glass of wine. By Wednesday morning it was full-on throbbing. By Thursday evening, when I had a champagne reception to go to, I was seriously thinking I would have to go home, I was so nauseous. I took some Nurofen before realising that there's two to three per cent caffeine in that too."

At ten o'clock in the evening, however, Carrie's headache disappeared. "Since then I haven't looked back," she smiles. "I feel cleaner. My sluggish feeling has disappeared. I've got lots more energy. I've stopped craving chocolate in the afternoon and I haven't craved coffee at all."

Naturally she feels better. She's put in the Zing! Coffee and tea are brown sluggish experiences that we use as a prop. People in control don't need caffeine. I bet Demi Moore has cut caffeine out of her life. Yet some scientists believe that Carrie's entire experience of ups and downs is psychological and that any benefits she feels will be due to her drinking much more water. "Tests have been conducted on this," says Wynnie Chan, Nutrition Scientist at the British Nutrition Foundation. "Two groups of people were both told they were being deprived of caffeine. Only one actually was, yet everyone experienced the same level of withdrawal symptoms. You can't get addicted to caffeine. You don't need more and more of it to have the same effect."

A British Nutrition Foundation conference on caffeine, held earlier this year, made clear that rather than being an enemy, it was actually quite a good thing. A strong tea or coffee in the morning (containing roughly 60mg of coffee) promoted clearheadedness, alertness and psychomotor performance. Further cups did not add to this effect but starting again in the afternoon helped the post-lunch dip. No links between caffeine and serious disease have been established. It doesn't give you cancer, it doesn't give you heart disease. About the worst thing you can throw at it, is that it can give you a bit of a headache if you overdo it. People's sensitivity to caffeine is obviously immensely varied. And there are some who don't feel good on caffeine yet continue to drink it. It's worth thinking about cutting down or out if you are:

a) Sensitive to caffeine and it gives you dodgy bowels

b) Drinking more than eight cups of caffeine-strong drinks a day

c) Catholic or like to be deprived of something on a regular basis

Jacqui Rogers, a medical herbalist at the London Clinic of Phytotherapy, says that there are a number of ways that one can achieve the coffee effect more naturally. "A lot of the benefits of coffee are psychological and it's a question of changing your habits. If you think caffeine gets you up in the morning, try instead a sniff of an invigorating essential oil like rosemary, lemon balm or peppermint - which are very uplifting. Avena Stevia is made of oats which are very rich in B vitamins; you can eat it as a porridge or take it as a tincture. Hot water with lemon juice (zing!) encourages peristaltic action (ie moves the bowels - essential if you have relied on your morning coffee to do the job). I wouldn't recommend decaffeinated drinks because they have been through chemical processes which make them less healthy. But if you like the coffee taste, dandelion coffee, taken with milk, is a nice sweet drink. Barley cup has a chicory taste that is quite nice."

Strangely, I find myself getting symptoms of irritability just at the thought of dandelion coffee. But then my attempts to give up caffeine never survive day one. I'm not so convinced that the psychological uplift from my new purity would outweigh the annoyance of not being allowed a daily fix. But I still want Zing! So I compromise. I have a hot water and lemon on waking up and drink it while the strong black coffee's brewing.