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understand this you need to realize that your body is an immensely complex

structure built from chemicals that must be regulated in order to function

smoothly. Chemicals such as hormones and other molecular messengers usually make

these adjustments. Medicines often work by taking the place of one of the

body’s regulating chemicals to readjust the balance. When this restores

two things complicate the picture. First, the body often uses the same chemical

to regulate more than one process. This means that a medicine may retune not

only the desired target but also others that don’t need readjustment. An

example of this is that the drug prednisone turns off inflammation, but also

causes thinning of bones. Secondly, medicines are not always as selective as we

would wish. This means the medicine may alter a number of unrelated processes at

the same time. For example, the antidepressant drug amitriptyline can help

depression (by acting on serotonin receptors), can also lower blood pressure (by

affecting norepinephrine receptors), cause blurred vision, dry mouth and

constipation (by blocking acetylcholine receptors) and produce sleepiness and

of the more surprising aspects of medications is how two people taking the same

medicine can have such different experiences. One person may have severe or

troublesome side effects that make the medicine intolerable, while another

person finds that the medicine does only the good that it is intended to do. In

fact when many thousands or millions of people use medicines, the list of

effects may be rare or common, serious or merely annoying. A medicine with

frequent mild side effects may be tolerated by the majority of people and be

regarded as relatively safe. On the other hand if a medicine has a less common

but more serious side effect it can mean that the medicine should only be used

when there is no alternative, and then with close monitoring. These

considerations require doctors to assess the risk of side effects versus the

expected benefit of any medication. In a life-threatening disease, even serious

side effects may be worth the risk; but for a mild, transient illness, little

we learn more about the way our bodies are regulated, more medications are

developed that allow us to intercede when diseases disrupt our functioning. It

has been a prominent goal in the development of new medications to avoid more

serious side effects. But it is likely that until we can foretell who is

especially susceptible, at least some people may experience side effects

from otherwise beneficial medications. Many of us may have to keep going back to

our doctors to try a second or even a third medication before we find one with

consult your health care provider before taking medication.