Some drugs act just by relieving symptoms-for example “pain killers”.
Others replace deficiencies in the body-iron tablets used to treat one sort of
anaemia. Others still kill off bacteria-antibiotics. Most drugs used to treat
heart conditions adjust the working of the heart or circulation rather like a
mechanic tuning an engine which is not functioning as well as it should.
The body has numerous control mechanisms, and altering the “volume”
of one mechanism with a drug may alter the setting of other mechanisms.
Often, too, a drug has more than one direct action. Doctors have to take
this into account when choosing a drug and adjusting its dosage for the best
overall result.