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Tea or coffee is often the favoured brew for those who are tired and in need of a caffeine boost. But is this really the best way to make ourselves more alert? Michael Mosley tested caffeine against some unlikely alternatives - sage, fudge, chewing gum and electric shocks.

How effective is caffeine for improving alertness? I drink lots of tea and coffee, so I assumed the answer is "very". But it is always worthwhile having your assumptions challenged.

So the Trust Me team asked Professor Peter Rogers of Bristol University to put caffeine to the test. He recruited a group of 20 people, 10 of whom never normally touch caffeine. The other 10, regular caffeine imbibers, were asked to turn up for testing having abstained for at least 12 hours.

Both groups were measured for mental agility, concentration and dexterity. Then they got a drink with a good jolt of caffeine in it. I found the results surprising, not to mention disappointing.

"Overall, regular caffeine consumers who'd been without caffeine overnight, were slower on the reaction time task, were sleepier and were less mentally alert than non-users," Professor Rogers said.

They did improve after they got a caffeine drink, but only up to the level the non-users had achieved without caffeine.

Find out more You can watch Trust Me, I'm a Doctor, with Michael Mosley and others, on iPlayer

When the non-users were given caffeine to drink their reaction times increased but they also became more jittery and anxious.

Professor Rogers says that, contrary to what most people believe, drinking lots of coffee on a regular basis won't enhance your mental performance. Part of the problem with caffeine is we quickly develop dependency.

So if you want to give your brain a boost, what else is out there?

Next we asked Dr Andy Johnson, of Bournemouth University, to test the impact on afternoon drowsiness of eating sugar, sage (the herb) and chewing gum.

He lined up 24 volunteers and in the morning did some tests to measure alertness. Then, in the afternoon, our volunteers were randomly allocated to either chew gum, eat fudge, swallow a pill containing sage or a placebo.

One hour later they did some really boring tests. They repeated this process three more times over the course of the week, each time trying something different.

As expected, swallowing a placebo pill made little difference. The volunteers still felt drowsier in the afternoon. Eating fudge, if anything, made them feel slightly worse.

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Chewing gum, surprisingly, improved mood, possibly because chewing seems to increases blood flow to brain. Going for a brisk walk would probably be just as effective.

In fact, the only thing in our test that really did seem to improve our volunteers' performance was the sage pills. This was not as unlikely as it might sound. There was a recent systematic review of clinical trials "assessing pharmacological properties of Salvia species on memory, cognitive impairment and Alzheimer's disease".

The review looked at eight studies which have tested the effects of sage on things like memory. Six of these trials involved normal subjects and two were done on people with Alzheimer's.

The researchers concluded that extracts of sage can enhance cognitive performance and it is safe, but they also caution that because so many different herbal preparations were used (extracts, essential oils, raw sage) better-designed trials are needed to establish which preparation is best.

The reason sage may have an effect is because it contains a cholinesterase inhibitor, a chemical which prevents the breakdown of the neurotransmitter, acetylcholine. Low levels of acetylcholine in the brain have been linked to memory problems. It is obviously only early stages of research into this herb, but there are clearly some interesting avenues for further research.

The final thing I wanted to test was electric shocks. Is it safe to shock your brain? For some years scientists have been using tDCS (transcranial direct current stimulation, a small electrical charge to the skull) to try to improve a whole range of things, from learning to reaction times.

Dr Charlotte Stagg of Oxford University, has been using it to help people recover strength in their hands after a stroke. Charlotte has found that, compared with a sham treatment, tDCS seems to speed up recovery, probably because of the effect that tiny electric currents have on neuronal connections inside the brain.

To see what effect it would have on me, Dr Stagg carefully positioned some electrodes on my skull and turned on the machine.

There was a slight itchiness and it did feel as if my brain had been given a jolt, but had it actually made any difference?

The short answer is yes. In a test which involved pressing a button when I saw a light go on, my reaction times improved from an average of 650 milliseconds before the machine was turned on, to 550 milliseconds with it on. These findings are in line with results from other subjects.

tDCS is currently being tested, not just as a way of helping people recover from stroke, but also as a potential treatment for depression. Charlotte is concerned, however, that people don't turn to homemade devices or machines you can buy on the internet.

"We do our studies in a very measured way," she told me "but we just don't know what the long term consequences of prolonged, uncontrolled use are likely to be."

Trust Me I'm a Doctor is on BBC iplayer

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