Which medicines are safe?

A totally safe and still fully effective medicine does not exist. Even penicillin, which has saved millions of lives can cause severe allergies, which can be deadly.

All drugs have an effect on our body: part of the effect is desired (to prevent, treat or cure a given disease, or ameliorate its symptoms), but part of the effects may be undesired (adverse events). A medicine is authorised to be used in humans when experts estimate that the desired effects on the disease outweigh the undesired effects on your body.


A patient took his medicine with lunch. He then suffered nausea/vomiting. Was this due to his food being spoiled? Or was it due to the medicine? This event is an adverse event, undesired, but without more information, no conclusion can be drawn and it is not certain whether it was a drug effect.

  • When you do not feel well right after taking a medicine, it may or may not be caused by the medicine. When the effect that you did not desire occurs, it is named an “Adverse Effect”, or “Undesired Effect”. Sometimes it is called a “Side Effect”, “Adverse Event”, or “Undesired Event”, or the term “Suspected Adverse Reaction”.
  • It is only when it is certain that the undesirable effect is due to the medicine that the term “Adverse Drug Reaction” applies. Literally, this means healthcare professionals have established that the undesired effect is a direct reaction to the drug.

When experts decide to authorise a medicine, they still wish to learn more about the effect of the medicine as more patients start taking it. When more patients than expected report the same undesired events, and it can be proven that the medicine is the cause, then the experts may revise their decision, adopt measures to diminish the risks when possible, or ultimately decide to withdraw the drug from the market if the effect is severe.

It cannot be guaranteed that all risks are known at the time a medicine first enters the market. It is likely that some risks will only become known after a medicine receives market approval.

For these reasons, rather than talking about the “safety profile” of a medicine, it is more accurate to use the term “toxicity profile” as all drugs come with some degree of risks.


Page created: 16/01/2013
Page last updated: 07/11/2014
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