Thank God for tea! What would the world do without tea? — how did it exist? I am glad I was not born before tea.

— Sydney Smith (1771-1845), English clergyman, writer, and wit

Stimulants are drugs that make people feel more alert and energetic by activating or exciting the nervous system. There are many stimulant drugs in current use; some are plants found in nature, others are chemicals made in the laboratory. These different drugs produce somewhat different effects, lasting for varying lengths of time, but all of them raise the energy level of the nervous system in roughly the same way.

The individual nerves in our bodies communicate with each other both electrically and chemically. A nerve impulse is an electric discharge that moves quickly along the fiber of a nerve cell. The fiber may end at a muscle, a gland, or another nerve cell, but there is always a tiny space between the end of the nerve fiber and the next cell. To bridge this gap, the nerve fiber releases small amounts of powerful chemicals called neurotransmitters that affect the next cell. Some neurotransmitters are strong stimulants that cause muscle cells to contract, gland cells to secrete, and other nerve cells to fire off electrical discharges. The most common stimulant neurotransmitter is a chemical called noradrenaline or norepinephrine. This chemical is closely related to the hormone adrenaline (or epinephrine), which is produced by our adrenal glands.*

'Adrenal is a Latin word meaning "on the kidney," because the adrenal glands sit on top of the kidneys like little caps. Epinephros means the same thing in Greek. In America the Parke-Davis pharmaceutical company succeeded in registering Adrenalin as a trademark for its brand of adrenal hormone, and as a result American scientists generally use the more cumbersome words epinephrine and norepinephrine. We prefer the Latin form.

Stimulant drugs work by causing nerve fibers to release noradrenaline and other stimulating neurotransmitters. Although different stimulants bring about this release in different ways, the end result is always the same: the release of more stimulating neurotransmitters. So, the stimulation people feel when they take stimulant drugs is simply a result of the body's own chemical energy going to work in the nervous system. The drug just makes the body expend it sooner and in greater quantity than it would ordinarily.

This release of chemical energy in the form of noradrenaline causes certain predictable changes in the mind and body. It makes a person feel wakeful, alert, and, often, happy. It makes the heart beat faster and may cause the blood pressure to rise. Because it produces changes in blood flow, the fingertips and tip of the nose may become cold. It gives a feeling of butterflies in the stomach and may cause a laxative effect.

Some of these changes are mediated by a branch of the nervous system called the sympathetic nervous system. The main function of the sympathetic nervous system is to respond to emergencies by preparing the body for fight or flight. It does so by shutting down nonessential functions and speeding up vital ones. The sympathetic nervous system relies on noradrenaline as its chemical messenger.

Now, noradrenaline acts in many of the same ways as adrenaline, the hormone secreted by the adrenal glands, also in response to emergencies. Experiences that cause the adrenals to secrete adrenaline into the bloodstream produce feelings very much like those of stimulant drugs. The rush of excitement one gets on a roller coaster ride, for example, may feel a lot like the effect of a dose of amphetamine, and no doubt both these techniques are popular for the same reason — because they give people a sense of increased mental and physical energy, and make them feel, temporarily at least, more alive.

In recent years scientists have begun to find out many interesting things about biorhythms, the cycles by which our vital processes wax and wane. The most obvious daily biorhythm is that of sleeping and waking. Production of hormones and neurotransmitters has its own ups and downs, and these cycles probably explain why people feel naturally stimulated at certain times and naturally lethargic at others. A common pattern is to feel energetic and able to concentrate well in the morning but to become tired and mentally sluggish in the late afternoon.

One reason that stimulant drugs are popular is that they give temporary control over rhythms of wakefulness and the ups and


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