How Common Are the Side Effects of Medicines?

We’ve all seen the alarming labels. “Warning: this product may cause catastrophic side effects that seem disproportionately severe for the medication you’re about to take” and it may have caused us all to worry a bit before taking whatever medicine the doctor gave us. But just how often do these side effects occur? In this article we’re going to look at three popular household medicines that are available over the counter to see how frequent adverse reactions to them really are, how severe the possible reactions are and take a look at the studies which found the issues.


Sildenafil citrate, the main active ingredient in the popular medicine Viagra, is used to treat erectile dysfunction (ED), although it was initially discovered by Pfizer in 1989 whilst looking for a treatment for heart-related chest pain, before being approved for medical use in Europe & The USA in 1998. It is used by millions of men in over 110 countries and is one of the best studied pharmacological substances available. Although it is generally effective and well-tolerated, common side effects of sildenafil can include:

  • Headache
  • Nausea
  • Flushing
  • Dizziness
  • Dyspepsia (indigestion)
  • Nasal congestion
  • Visual disturbances




Improves male’s sexual performance
Increases body’s production of Nitric Oxide levels
Spark male’s interest in sex

Possible risks

Can cause mild headache


60 Capsules


2 Capsules per day

Enough for

30 days





How common are sildenafil side effects

Out of 14 clinical trials (consisting of 3780 men in total), the most common adverse reactions to were flushing (12%), headache (11%), dyspepsia (5%), and visual disturbances (3%). Another separate study found that frequent side effects included dizziness (8.8%), Dyspepsia (6.5%), and nasal congestion (5.4%)

Of course, the percentage of men who experience adverse reactions to sildenafil will vary from study to study. This is because variables – such as sample size and sampling methods – usually differ between trials. However, the data seems to show that sildenafil is typically well-tolerated, with low numbers of men experiencing adverse effects. To learn more about the side effects of sildenafil, click here.


Chances are that if you’ve ever had a cracking headache, you’ve probably taken paracetamol to relieve the pain. First made in 1877 paracetamol has become the most commonly used medication for pain & fevers in both the United Sates and in Europe and it is listed on the World Health Organisation’s list of essential medicines, showing just how essential this medicine is for pain relief around the world.

It’s not exactly known how paracetamol works (and recent evidence suggests its effects are, in fact, negligible), but it is believed to work by blocking the chemical messengers in the brain that tell us we have pain, in order to provide relief for light to mild pain.

Serious side effects are rare, however some of the common side effects of paracetamol are:

  • An allergic reaction (characterised by rash and swelling)
  • Flushing
  • Low blood pressure
  • Fast heartbeat
  • Blood disorders (thrombocytopenia and leukopenia)
  • Liver and kidney damage
  • Gastrointestinal disorders (diarrhea, dyspepsia, nausea, etc.)
How common are paracetamol side effects?

In one 300 patient-strong test by Vanderbilt University in 2004, 28% of the patients experienced an adverse reaction to paracetamol. Specific side effects – and how often they occurred – were reported as follows:

  • Upper respiratory tract infection (5.7%)
  • Diarrhea (4.7%)
  • Headache (3.7)
  • Dyspepsia (2.3%)
  • Nausea (1.3%)
  • Flatulence (1.3%)


Dextromethorphan (DXM) is most commonly found in prescription cough medicines, but it can also be found in cold and flu medication. It is an antitussive, meaning it suppresses coughs by inhibiting the cough reflex. Much like sildenafil, it has been widely studied and is reported to have infrequent adverse effects. Negative reactions to DXM usually occur when the user has taken more than the recommended amount.

Nonetheless, side effects of DXM include:

  • confusion
  • constipation
  • dizziness (mild)
  • drowsiness (mild)
  • headache
  • nausea or vomiting
  • stomach pain
How common are dextromethorphan side effects?  

In one small study, DXM was shown to have very few adverse effects. The most commonly reported side effects were hyperactivity (18%), insomnia (9%), stomachache/nausea (6%), dizziness (3%) and nervousness (3%). There were no reports of drowsiness, headache, or disorientation (confusion). This is not to say that these more mild side effects do not occur, however. Indeed, they do – but they are rare, especially when DXM is administered according to Doctors orders. As the severity of side effects of DXM depend on the dosage consumed, adverse effects are likely to be more common (and more severe) with higher dosages.

The Verdict  

Based on the available evidence, it appears adverse reactions to these household medicines are infrequent and often only mild when they occur. While each has its own range of side effects, the most common side effects seem to be relatively uncommon and mild in severity. Nonetheless, before attempting to take any medication, check with your doctor to ensure the medication is safe for you to take and does not conflict with any medication you are already on.


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Written by HealthStatus Crew
Medical Writer & Editor

HealthStatus teams with authors from organizations to share interesting ideas, products and new health information to our readers.

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