Over-the-counter medicines are sold without a prescription because they are considered reasonably safe for self-treatment of a recognisable, short-lived problem. That is not the same as harmless. Being able to buy something off a shelf says something about how it is regulated, not about whether it is safe alongside your other medicines or your particular health conditions.
Most real harm from pharmacy medicines comes from three things rather than from the medicines being dangerous in themselves: taking the same ingredient twice without realising, taking something for longer than intended, and combining a pharmacy product with a prescription medicine.
Common side effects of this pharmacy medicine or category
By category, the effects that come up most often:
- Pain and fever. Stomach irritation from anti-inflammatories; drowsiness and constipation from codeine-containing combinations. See pain and fever medicines.
- Cold, flu and sinus. Jitteriness, palpitations and raised blood pressure from decongestants; drowsiness from sedating antihistamines. See cold and flu medicines.
- Allergy. Drowsiness and dry mouth, mainly from older antihistamines. See antihistamines.
- Stomach and bowel. Constipation from anti-diarrhoeals, cramping from laxatives, and rebound symptoms after prolonged use of acid remedies. See stomach medicines.
- Skin preparations. Irritation, and skin thinning with prolonged steroid cream use. See topical medicines.
Interactions and duplicate-ingredient risks
Duplicate ingredients are the most common avoidable problem with pharmacy medicines. Paracetamol in particular appears in combination painkillers and in cold, flu and sinus remedies, so taking a plain paracetamol tablet alongside a flu remedy can double the dose without either pack looking like a painkiller.
The habit that prevents it: read the active ingredients panel on every product before combining anything, and treat brand names as unreliable guides to what is inside. See taking two medicines that both contain paracetamol.
The other frequent pattern is a pharmacy product working against a prescription medicine: a decongestant raising blood pressure that is being treated, or an anti-inflammatory reducing the effect of blood pressure tablets and straining the kidneys. See OTC medicines alongside chronic medication.
Children, pregnancy, older adults and chronic medicine cautions
- Children. Doses go by weight, syrups come in different strengths, and some products are not suitable at all. See children and OTC medicines.
- Pregnancy and breastfeeding. Ask before buying anything. See OTC medicines in pregnancy.
- Older adults. Higher risk of stomach bleeding, kidney effects, drowsiness and falls. See OTC medicines in older adults.
- Existing conditions. Asthma, kidney or liver disease, high blood pressure, heart failure, ulcer history and glaucoma all change what is suitable.
Warning signs and overdose concerns
Get emergency help for:
- Difficulty breathing, wheeze, or swelling of the face, lips or throat
- A rash that blisters or peels
- Vomiting blood, or black tarry stools
- Severe or sudden abdominal pain
- Chest pain, fainting, or a racing heartbeat
- Confusion or drowsiness that is out of character
Suspected overdose is an emergency even when the person feels well. This matters most with paracetamol, where serious liver damage can be underway for a day before any symptom appears, and treatment works best when started early. Go to an emergency unit and take the packaging. See paracetamol overdose symptoms.
Questions to ask a pharmacist before using it
- Is this suitable with my other medicines and conditions?
- Does anything else I take contain the same ingredient?
- How many days can I use it before I should see a doctor?
- Is there a simpler single-ingredient option instead of a combination?
- What is the correct dose for my child’s weight?
Bring a list of everything you take, including supplements. A pharmacist can only screen for problems they know about.
Related OTC and medicine-safety guides
- Over-the-counter medicine interactions
- How to read over-the-counter medicine labels
- When to see a doctor about an OTC medicine
- Medication side effects hub
- Report an OTC medicine side effect in South Africa
Medical Disclaimer: This content is for informational and educational purposes only and does not constitute medical diagnosis, prescription, or professional advice. Always read the patient information leaflet and consult a qualified doctor or pharmacist regarding any medicine or health concern.