Medicines, supplements and other health products can cause unwanted effects. Many side effects are mild, such as nausea, dry mouth, dizziness or drowsiness, but some symptoms may signal a serious reaction that needs urgent medical assessment. A symptom that starts after taking a medicine may be related to it, but timing alone does not prove that the medicine is the cause.
If you are having trouble breathing, severe chest pain, swelling of the face or throat, heavy bleeding, a seizure, fainting or loss of consciousness, a severe blistering or peeling rash, or thoughts of harming yourself or someone else, seek emergency medical help now. In South Africa, you can call 112 from a cellphone or 10177 for emergency medical care. Do not wait for an online side-effects check if symptoms appear life-threatening.
If the symptoms are not an emergency, this guide can help you understand what to track and what to discuss with a doctor or pharmacist. You can also browse the Symptom-Led Side Effects hub for other symptom-specific guides.
How urgent Help Medication Side Effects can be linked to medicines or supplements
A medicine side effect is an unwanted effect that happens while a medicine is being used. Side effects can occur with prescription medicines, over-the-counter products and, in some cases, supplements or combinations of products.
Some reactions happen soon after a dose. Others may develop after several days or weeks. The timing depends on the medicine, the type of reaction and the individual taking it. A new symptom may also have a cause that has nothing to do with the medicine, so it is important not to diagnose the cause based on timing alone.
Timing clues
Information about timing can still be useful to a healthcare professional. Tell your doctor or pharmacist if the symptom appeared after you started a new medicine, after the dose changed, after restarting a medicine, or after adding another prescription, over-the-counter medicine or supplement.
Also mention whether the symptom happens shortly after each dose, whether it is getting worse, and whether you have had the same reaction to the medicine or a similar product before.
Serious allergic reactions such as anaphylaxis can develop quickly and may cause throat or tongue swelling, difficulty breathing or swallowing, wheezing, dizziness, confusion or fainting. Medicines are among the substances that can trigger anaphylaxis.
For more information about symptoms that may indicate a significant reaction, see the related parent guide.
Medicines and product categories that may be associated with this symptom
There is no single category of medicine responsible for all urgent side effects. The warning signs depend on the medicine and the person taking it.
Possible medicine categories
Antibiotics and some anti-inflammatory medicines can, rarely, be associated with serious allergic reactions. Certain medicines are also associated with rare but serious skin reactions that cause blistering, painful sores or peeling skin. NHS guidance notes that Stevens-Johnson syndrome is often linked to certain medicines, including some epilepsy medicines, antibiotics and anti-inflammatory painkillers.
Opioid pain medicines can cause dangerous breathing problems in some circumstances. For example, opioid medicines such as morphine can cause slowed breathing, long pauses between breaths or severe shortness of breath, with risk affected by factors such as dose and other substances or medicines being used.
Blood-thinning medicines can increase bleeding risk. Warning signs may include bleeding that does not stop, red or brown urine, red or black stools, vomiting or coughing up blood, unusual bruising, or dizziness and weakness associated with bleeding.
Insulin and certain other diabetes medicines can cause low blood sugar. Severe hypoglycaemia may lead to confusion, fainting, seizures or unconsciousness and requires immediate attention.
Some medicines also carry specific warnings about serious changes in mood or behaviour. These risks vary significantly by product and patient group, which is why the medicine’s professional information or patient leaflet and advice from a healthcare professional are important.
These examples are not a complete list. A pharmacist or doctor can check the specific product, dose, other medicines and supplements you use, and the timing of your symptoms.
Red flags: when this symptom may need urgent medical attention
Some symptoms should not be monitored at home while you wait to see whether they improve.
Red flags
Seek immediate emergency medical help for symptoms such as:
- difficulty breathing, very slow breathing, choking, severe wheezing or severe shortness of breath;
- sudden swelling of the lips, mouth, tongue, face or throat, particularly with breathing or swallowing problems;
- fainting, loss of consciousness, severe confusion or being unable to wake normally;
- a seizure;
- severe chest pain or chest pressure;
- heavy or uncontrolled bleeding, coughing or vomiting blood, or other signs of serious bleeding;
- a rapidly worsening rash with blisters, painful sores or peeling skin, especially if the mouth or other mucous membranes are affected;
- a suspected medicine overdose or taking substantially more than intended; or
- suicidal thoughts, an attempt to harm yourself, or an immediate risk of harm to yourself or someone else.
These warning signs are not proof that a medicine caused the problem. They are reasons to get urgent medical care regardless of the cause.
For more detail, read about serious medication side effects and when to see a doctor for medication side effects.
If you need emergency help in South Africa, call 112 from a cellphone or 10177 for emergency medical care.
What to track before speaking to a doctor or pharmacist
If your symptoms are not an emergency, keeping a clear record can help a healthcare professional assess what may be happening.
What to track
Write down the name and strength of every prescription medicine, over-the-counter medicine, supplement or herbal product you use. Include the dose you normally take and when you last took it.
Record when the symptom started, what it felt like, how long it lasted and whether it has become better, worse or stayed the same. Note any recent dose changes or newly added products.
Also tell your healthcare professional about relevant medical conditions, allergies and previous reactions to medicines. If there is a visible reaction such as swelling or a rash and it is safe to do so, a photograph may help document how it changed over time.
Keep medicine packaging, dispensing labels and patient information leaflets available. In an emergency, providing healthcare professionals with an accurate list of what has been taken can help them assess the situation.
What not to do without medical advice
A suspected side effect does not automatically mean that you should stop or alter a prescription medicine yourself.
What not to change without advice
Do not routinely reduce the dose, double a later dose, change the dosing schedule, restart a medicine after a significant reaction, or abruptly stop long-term treatment without guidance from an appropriate healthcare professional. Some medicines can cause problems if their dose is changed or they are stopped suddenly. Product-specific instructions differ.
If symptoms are severe or life-threatening, getting emergency medical care takes priority. Emergency clinicians can assess the reaction and decide how the suspected medicine should be managed.
Do not assume that a supplement or non-prescription product is irrelevant. Tell your doctor or pharmacist about everything you are taking because medicines and other products may interact, and an interaction can change the risk of adverse effects.
Related side-effect guides and reporting options in South Africa
If your symptoms are stable and not an emergency, you can review other side effect symptoms A-Z or read the main guide to medication side effects.
If you suspect that you experienced an adverse reaction to a medicine or health product, you can also learn how to report side effects in South Africa.
The South African Health Products Regulatory Authority (SAHPRA) maintains pharmacovigilance guidance for adverse drug reaction reporting. SAHPRA’s current healthcare-professional ADR reporting guideline is Version 4, dated 23 October 2025, and SAHPRA also provides the Med Safety reporting system through which patients and healthcare professionals can submit suspected adverse reactions.
Reporting a suspected reaction does not mean that the medicine has definitely been proven to cause it. Reporting helps medicine-safety authorities collect and assess information about possible adverse reactions.
Frequently asked questions
Is this a common side effect?
It depends on the specific medicine and symptom. Some effects, such as mild nausea, dizziness or drowsiness, can be relatively common with particular medicines, while reactions such as anaphylaxis or severe blistering skin reactions are uncommon but potentially serious. Check the official information for your medicine and speak to a pharmacist or doctor if you are unsure.
How long can a medicine side effect last?
There is no single timeframe. Some effects occur briefly around a dose, while others may persist or appear later. How long a symptom lasts depends on the medicine, dose, underlying health conditions and the cause of the symptom. Symptoms that persist, worsen or repeatedly return should be discussed with a healthcare professional.
Should I stop the medicine?
Do not make routine changes to prescription treatment without professional advice. The safest action depends on the particular medicine and reaction. If you have emergency warning signs, seek emergency medical care immediately so that clinicians can assess both the reaction and the medicine. Some medicines can also cause problems if they are stopped abruptly.
When should I seek help?
Seek emergency help immediately for breathing problems, swelling of the mouth or throat, severe chest pain, fainting or unconsciousness, seizures, major bleeding, suspected overdose, a severe blistering or peeling rash, or an immediate risk of self-harm. For symptoms that are not an emergency but are new, worsening, persistent or worrying, contact a doctor or pharmacist for advice.
Medical disclaimer: This information is for general education and does not diagnose a medicine reaction or replace advice from a doctor, pharmacist or other qualified healthcare professional. Side effects and urgent-care thresholds can vary according to the medicine and individual circumstances. If symptoms are severe, rapidly worsening or potentially life-threatening, seek emergency medical care immediately.