Wouldn’t it be nice if you could swallow a pill to help you pass exams, to remember all the names of the pupils in your new class, or to banish the forgetfulness that so often accompanies middle age? Who could fail to be tempted by “smart” drugs and nutrients that can improve memory, increase intelligence and restore concentration and alertness? Enthusiasts will tell you that there are more than 140 different chemicals, food additives or drugs that can perform one if not all of these tasks. But what are “smart drugs”, and do any of these substances that you see advertised in books, magazines and on the internet actually work?

Smart drugs are supposed to work in one of two ways: they either boost a brain chemical that might be involved in learning and memory processes, or increase blood flow to the brain. They are sometimes referred to as nootropics; a term coined by a pharmacologist in the Seventies from the Greek “noos” meaning mind and “tropos” meaning changed or toward.

Today the most famous - or infamous - smart drugs are probably Prozac, typically prescribed as an antidepressant, and Ritalin for attention deficit disorders. But one of the earliest, and still the most widely advertised, is piracetam, which boosts the production of the brain chemical acetylcholine. In the 1970s, postmortem studies on the brains of people who had died from Alzheimer’s disease showed they had suffered a dramatic loss of brain cells, particularly those that produce acetylcholine. Around the same time, research on animals indicated that acetylcholine was a key brain chemical in memory formation. So, if loss of acetylcholine was responsible for memory loss, why not try to increase its supply to the brain?

Thus piracetam, as well as food additives such as choline, acetlycarnosine and DMAE (dimethylaminoethanol) - which may all increase the production of acetylcholine - is classed as a smart drug. But a single brain chemical could not be solely responsible for intelligence and memory, so the search widened to take in drugs or food additives that could target other brain chemicals such as glutamate, serotonin and dopamine.

Studies on stroke patients then prompted the idea that drugs that increase blood flow to the brain could also be “smart”. Stroke sufferers can lose many aspects of performance, including memory, because brain cells may be starved of blood. Propanolol, phenytoin and hydergine - smart drugs all - increase blood flow to the brain.

While the rationale for these drugs may be plausible, where is the hard scientific evidence that they work? Studies on mice and rats show that when certain drugs are injected in high doses they accelerate learning of specific tasks, such as negotiating a maze for a food reward. (It has to be assumed that the drug does not simply increase the animal’s appetite or general level of physical activity.) In human studies, the same or similar drugs have been claimed to improve IQ and memory tests. Unfortunately, such studies have been poorly controlled and they are typically carried out on a small number of patients. Most have been done in southern Italy, where ethical controls and statistical procedures are far less rigorous than in the UK and the US. So most scientists view the evidence for cognitive enhancing drugs with scepticism, while acknowledging the undoubted progress that has been made with the treatment of Alzheimer’s.

Today, more than 200 smart drugs are being developed for the treatment of Alzheimer’s. The problem is that advocates not only advertise the nootropic drugs that alter brain chemistry or brain blood flow, but a range of other drugs and herbs that have little or no clinical credibility as memory boosters. For example, vasopressin, a drug that merely helps the body to retain water, is listed on the internet as a smart drug.

Then there is melatonin. This is a hormone secreted during the night that can be used to treat symptoms of jet lag. It is not available in the UK, but is an over-the-counter drug in the US. There are other “remedies” such as ginseng and ma huang, sex steroids and growth hormones, but promoting them as memory boosters is absurd.

A quick surf on the web could convince any committed consumer that there are quick chemical fixes for poor or failing memory and recall. Most, if not all, smart drugs are available over the internet without prescription, even though some of them can be dangerous when taken without supervision or professional advice. It is clear that there is no credible scientific evidence to justify the claim that smart drugs can boost the memory of a healthy individual. Better to keep our brains active rather than think there’s a drug out there that will keep us smart.

Saffron Davies is a senior lecturer at St George’s Hospital medical school, south London