Yes. Medicines, over-the-counter products and supplements can sometimes cause serious side effect symptoms. Most medicine side effects are not medical emergencies, but certain symptoms can signal a severe allergic reaction, bleeding, organ injury, a dangerous change in heart or brain function, or another reaction that needs urgent assessment.
The important question is not only whether a symptom could be caused by a medicine, but also how severe it is, when it started and whether other warning signs are present.
If you are having trouble breathing, swelling of the face or throat, chest pain, uncontrolled bleeding, a seizure, loss of consciousness, a severe blistering or peeling rash, or suicidal thoughts, seek emergency medical help immediately. In South Africa, you can call 112 from a mobile phone or 10177 for ambulance services.
For a broader overview of symptoms that may occur with medicines, visit the Symptom-Led Side Effects hub.
Medical safety note: This information is for general education and cannot determine whether a medicine caused your symptoms. Serious or rapidly worsening symptoms should be assessed by a healthcare professional. Do not delay emergency care while trying to identify the medicine responsible.
How serious Side Effect Symptoms can be linked to medicines or supplements
A side effect is an unwanted effect that occurs while using a medicine or health product. Some effects are expected and relatively mild, while others are uncommon but potentially serious.
Symptoms may appear:
- soon after taking a medicine;
- after the dose has been increased;
- after several days or weeks of treatment;
- when more than one medicine or supplement is being used;
- when a medicine interacts with alcohol, another medicine or an underlying health condition;
- after taking more than the recommended amount; or
- occasionally after a medicine has been used without previous problems.
The timing can provide an important clue, but it does not prove that the medicine caused the symptom. Illnesses, infections and other medical conditions can produce similar symptoms.
Timing clues
When speaking to a doctor or pharmacist, consider whether the symptom started after:
- beginning a new prescription medicine;
- changing the dose;
- adding an over-the-counter medicine;
- starting a vitamin, herbal product or supplement;
- changing brands or formulations;
- receiving an injection or other treatment; or
- accidentally taking an extra dose.
An unexpected symptom after a medicine change deserves particular attention if it is severe, rapidly worsening or accompanied by other warning signs.
If you are unsure whether a symptom is medicine-related, a healthcare professional can review the timing, dose, other medicines you use and your medical history.
Medicines and product categories that may be associated with this symptom
There is no single group of medicines responsible for all serious reactions. Different products carry different risks, which is why the professional information or patient leaflet for the specific medicine matters.
Possible medicine categories
Examples of medicine-related problems that may need urgent medical assessment include the following.
Allergic reactions and anaphylaxis: Almost any medicine can potentially cause an allergic reaction in a susceptible person. Severe reactions may involve sudden swelling of the lips, tongue, mouth or throat, difficulty breathing or swallowing, wheezing, dizziness, confusion or collapse. These can be features of anaphylaxis and require immediate medical treatment.
See our guide to anaphylaxis from medicine symptoms for more information.
Bleeding: Anticoagulants and medicines that affect blood clotting can increase bleeding risk. Some non-steroidal anti-inflammatory drugs, or NSAIDs, can also cause gastrointestinal bleeding. Warning signs can include vomiting blood, black or bloody stools, feeling faint or persistent abdominal pain.
Read more about medicine causing bruising bleeding and NSAIDs stomach bleeding symptoms.
Severe skin reactions: Rare reactions such as Stevens-Johnson syndrome can occur after certain medicines, including some anti-seizure medicines, antibiotics and anti-inflammatory medicines. A spreading painful rash, blistering, peeling skin or sores affecting the mouth or eyes needs urgent assessment, particularly after starting a new medicine.
Liver problems: Certain prescription and non-prescription medicines can injure the liver. Symptoms associated with drug-induced liver injury can include yellowing of the skin or eyes, dark urine, abdominal pain, loss of appetite and unusual tiredness. Taking more than the recommended amount of medicines containing paracetamol can be particularly dangerous to the liver.
See medicine causing liver problems for more detail.
Kidney problems: Some medicines can contribute to acute kidney injury, especially in people who are dehydrated or who already have kidney disease or other risk factors. NSAIDs are one example. Possible signs of acute kidney problems include a marked reduction in urine, swelling, shortness of breath, persistent nausea or vomiting, severe tiredness or confusion.
Changes in mood or behaviour: Certain medicines have specific warnings about psychiatric effects. For example, some antidepressants carry warnings about new or worsening suicidal thoughts or behaviour in particular age groups, especially early in treatment or after dose changes. Any suicidal thoughts or immediate risk of self-harm require urgent help.
These examples are not a complete list. Always check the patient information supplied with your medicine and ask a pharmacist or doctor if you are uncertain about a warning.
Red flags: when this symptom may need urgent medical attention
A symptom should be treated as urgent when it suggests a potentially life-threatening reaction or when the person’s condition is deteriorating quickly.
Red flags
Seek emergency medical help immediately for symptoms such as:
- difficulty breathing, severe wheezing or a feeling that the throat is closing;
- sudden swelling of the lips, mouth, tongue, face or throat;
- fainting, collapse or being unable to wake someone normally;
- severe confusion or a major change in consciousness;
- chest pain or severe difficulty breathing;
- a seizure;
- bleeding that will not stop;
- vomiting blood or passing black or bloody stools;
- a rapidly spreading, painful, blistering or peeling rash;
- painful sores or blisters affecting the mouth, eyes or genitals;
- suicidal thoughts or an immediate risk of self-harm; or
- symptoms following a suspected medicine overdose.
Difficulty breathing, uncontrolled bleeding, seizures, loss of consciousness and suicidal intent are recognised warning signs of medical emergencies. Severe allergic reactions and serious skin reactions can also require immediate hospital treatment.
For more guidance, see serious medication side effects and when to see a doctor for medication side effects.
If the situation appears life-threatening, do not wait for an ordinary doctor’s appointment. In South Africa, call 112 from a mobile phone or 10177 for an ambulance, or go to an appropriate emergency department.
Our urgent help medication side effects guide provides further information about deciding when immediate medical care may be needed.
What to track before speaking to a doctor or pharmacist
For symptoms that are not an immediate emergency, collecting a few details can make it easier for a healthcare professional to assess what may be happening.
What to track
Write down:
- the name of every prescription medicine you take;
- the names of over-the-counter medicines, vitamins, herbal remedies and supplements;
- the dose and how often each product is taken;
- when each medicine was started;
- any recent dose increases or decreases;
- when the symptom first appeared;
- whether it occurs shortly after a dose;
- whether it is becoming better, worse or staying the same;
- any other symptoms occurring at the same time; and
- any recent illness, dehydration, alcohol use or other relevant changes.
If possible, take the medicine packaging, patient leaflet or an up-to-date medicine list to your appointment. This can help a pharmacist or doctor identify duplicate ingredients, possible interactions and products that may require closer review.
Do not assume that an over-the-counter product or supplement is irrelevant. Include everything you are taking, even if you use it only occasionally.
Photographs may also be useful for symptoms such as a rash, swelling or bruising, provided taking a photograph does not delay medical attention.
What not to do without medical advice
When people are worried about a possible reaction, it is understandable to want to change their treatment immediately. However, altering some medicines suddenly can create additional risks.
What not to change without advice
Unless an emergency healthcare professional or the medicine’s official instructions tell you otherwise:
- do not abruptly stop a prescription medicine simply because a symptom appeared;
- do not reduce or double the dose on your own;
- do not take an extra dose to “make up” for a missed dose unless the instructions specifically say to do so;
- do not add another medicine to treat the symptom without checking for interactions;
- do not restart a medicine that previously caused a suspected serious allergic reaction without medical advice; and
- do not assume that a natural, herbal or over-the-counter product is automatically safe to combine with prescription treatment.
A doctor or pharmacist may need to decide whether the medicine should be continued, changed, temporarily withheld or replaced. That decision depends on the medicine involved, the reason you take it and the nature of the reaction.
If symptoms are severe or emergency warning signs are present, getting medical help takes priority over trying to manage the reaction yourself.
For general information about medicines and unwanted effects, see our guide to medication side effects.
Related side-effect guides and reporting options in South Africa
If you suspect that a medicine or health product has caused an unwanted reaction, discuss it with a doctor or pharmacist. They can assess whether you need treatment and whether the suspected medicine requires further review.
You can also report side effects in South Africa.
SAHPRA’s Med Safety system allows members of the public as well as healthcare professionals to report suspected adverse drug reactions. Reports contribute to ongoing monitoring of medicine safety in South Africa. A report is useful even though the suspected relationship still needs to be assessed; reporting a suspected reaction does not by itself prove that the medicine caused it.
Reporting is not a substitute for medical care. If someone is seriously ill, seek appropriate treatment first.
For other symptom-specific information, browse the side effect symptoms A-Z.
Frequently asked questions
Is this a common side effect?
It depends entirely on the medicine and the symptom. Some medicines commonly cause mild effects such as nausea, dizziness or headache, while severe reactions may be uncommon or rare. A symptom being uncommon does not mean it should be ignored when it is severe.
Check the official patient leaflet or professional information for the medicine, and ask a pharmacist or doctor if you are unsure how frequently a particular reaction occurs.
How long can serious side effect symptoms last?
There is no standard time. Some reactions improve quickly, while others can continue until the underlying problem has been assessed and treated.
Duration alone does not determine whether a symptom is dangerous. Sudden difficulty breathing, severe swelling, major bleeding, seizures, collapse or a severe blistering rash require urgent help even if they have only been present for a short time.
Should I stop the medicine?
Do not make an unsupervised change to prescription treatment unless the medicine’s official instructions or an emergency healthcare professional specifically direct you to do so.
Some medicines can cause problems when stopped suddenly, and a doctor or pharmacist needs to consider the suspected reaction alongside the condition being treated.
If you have emergency warning signs, seek immediate medical care rather than waiting for routine advice about the next dose.
When should I seek help?
Seek emergency help for breathing difficulty, swelling of the face or throat, chest pain, a seizure, collapse, uncontrolled bleeding, vomiting blood, black or bloody stools, a severe blistering or peeling rash, suicidal thoughts or other rapidly worsening symptoms.
For symptoms that are less severe but persistent, unusual or worsening, speak to a doctor or pharmacist. This is particularly important after starting a new medicine, changing a dose or adding another medicine or supplement.
Check possible medicine-related causes, track your symptoms and speak to a doctor or pharmacist if you are concerned. Serious or rapidly worsening symptoms should always be assessed promptly.