Drugs Q & A

Side Effects Vs. Adverse Effects Vs. Contraindications

Medical terminology is often poorly understood, especially by young and poorly educated patients. Even Educated people can sometimes find it pretty hard to fully grasp what a medication leaflet is trying to convey. A patient information leaflet (PIL) is usually included in every medicine package to offer written information about the medication. But some terminologies used in might sound confusing and sometimes conflicting.

Patient information leaflets consist of the same types of information for every medication. Their main purpose is to inform patients about their medication regarding its administration, precautions and potential side effects. Studies have shown that patients want straightforward information about their treatment. They are most likely to read leaflets about their medicine when it is first prescribed to them. The risk of side effects will have a big influence on whether they take their medication or not.

What is the difference between side effects, adverse effects and contraindications?

The terms “side effects” and “adverse effects” are often used interchangeably.  This may be correct in many contexts, but the two terms do not mean exactly the same thing.

Side effects are effects seen on the side in clinical use. These effects occur at clinical therapeutic doses. Side effects encompass any effects that are not the intended clinical effect of the drug, whether or not these effects are harmful or adverse.

Adverse effects in contrast, are any undesired harmful effects or effects that cause undesired outcomes. Adverse effects encompass not only those effects that occur at clinical therapeutic doses but also effects that can occur on overdose. However, the term adverse drug reaction specifically refers to unwanted or undesirable effects of a medication that occur during usual clinical use and so excludes overdose.  The harm resulting from adverse effects can be direct physical harm or toxicity. But an adverse effect can also be a secondarily harmful effect, for example, effects that cause adverse outcomes such as increased risk of noncompliance with the medication.

Thus adverse effects can be side effects when they are undesired harmful effects that occur alongside the desired therapeutic effect. Vice versa, side effects can be adverse effects when they are harmful. Moreover, because the definition of side effects relates to the intended clinical effect, the side effect or adverse effect in the context of clinical use for one condition can be a therapeutic effect when the same drug is used for another clinical condition. For example, when phenylephrine is used as a nasal decongestant, increased blood pressure is a side effect and indeed also an adverse effect because hypertension is potentially harmful. But when phenylephrine is used to treat hypotension, the increase in blood pressure is the desired therapeutic effect.

For example, research may have shown that a headache occurs in 1 in every 10 patients who use the drug according to the instructions. Heart palpitations may occur in 1 in every 100 patients.

Some common examples mild adverse effects related to drugs include:

  • Constipation
  • Diarrhea
  • Dizziness
  • Drowsiness
  • Dry mouth
  • Headache
  • Insomnia
  • Nausea
  • Skin rash or dermatitis

Examples of more serious effects include:

  • Abnormal heart rhythms
  • Cancer
  • Internal bleeding
  • Suicidal thoughts

Some effects are more likely than others. The PIL that comes with a drug or device will categorize effects according to their probability

It is important to check the PIL on getting new drugs, to find out what effects may occur and how likely these are. The PIL will also advise on whether an effect is classed as an emergency or not.

In the U.S., DailyMed provide information about drugs and their effects through the FDA. It offers an online source for patients to check for details of their medications.

Contraindication are symptoms or conditions that make a particular treatment or procedure inadvisable. In the context of pharmacology, we usually speak of contraindications when the regulatory authorities who assess drug safety and license the sale of drugs have required the manufacturer or supplier to include specific contraindications on the box or product insert. When a patient has these symptoms or conditions, the contraindicated drug should not be used for this patient.

According to a study in the British Journal of General Practice, current leaflets do not promote health literacy. Providing patients with good health information will to encourage participation in their health care and improve their understanding of medication safety and its associated benefits.

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