Doxycycline is a tetracycline antibiotic used for chest infections, acne, sexually transmitted infections, tick bite fever and malaria prevention. It must be taken sitting upright with plenty of water, and it causes marked sun sensitivity.
What is Doxycycline?
Doxycycline is a tetracycline antibiotic, dispensed as 50 mg and 100 mg capsules and tablets. It is a Schedule 4 prescription medicine, sold under its own name and as Doxytet, Cyclidox and Doximal.
It binds to the bacterial ribosome and blocks protein synthesis, so the bacterium cannot grow or multiply and the immune system clears the infection. Human ribosomes are structurally different, which is the basis of its selectivity.
Doxycycline is broad-spectrum, and it covers organisms many other antibiotics do not — including intracellular bacteria such as Chlamydia, Rickettsia (which causes tick bite fever) and Mycoplasma, because it penetrates into cells well.
Two features shape how it must be taken.
It can cause severe oesophageal irritation. A capsule that lodges in the gullet dissolves there and burns the lining, causing pain and ulceration. This is common, entirely preventable, and covered below.
It causes pronounced sun sensitivity. Burning after unusually short exposure is frequent, which matters a great deal in South Africa.
What is Doxycycline commonly used for?
- Chest infections, including atypical pneumonia and flare-ups of chronic bronchitis.
- Acne and rosacea, taken at a lower amount over months.
- Sexually transmitted infections — chlamydia (a seven-day course), and part of treatment for pelvic inflammatory disease and syphilis in penicillin allergy.
- Tick bite fever, where doxycycline is the treatment of choice in South Africa.
- Malaria prevention, taken daily by travellers to malaria areas.
- Skin and soft tissue infections.
- Sinusitis.
- Leptospirosis, brucellosis, cholera and other less common infections.
- Periodontal disease, at low doses.
Two uses are worth explaining.
Tick bite fever is common in South Africa and doxycycline treats it well. Suspect it after outdoor exposure with fever, severe headache, muscle aches, a rash, and often a black scab (an eschar) at the bite site. Treatment is usually started on suspicion rather than waiting for tests, and it works quickly.
Acne is a different kind of use entirely: a low amount taken daily for months, not a short course, and the benefit comes as much from its anti-inflammatory effect as from killing bacteria. It is used alongside topical treatment, and improvement takes six to twelve weeks — stopping at three weeks because nothing has happened is the usual mistake.
For malaria prevention, it must be started before travel, taken every day during, and — critically — continued for four weeks after leaving the malaria area.
How Doxycycline fits into this medicine category
| Group | Examples | Common targets |
|---|---|---|
| Tetracyclines | Doxycycline, lymecycline | Chest, acne, STIs, tick bite fever, malaria prevention |
| Broad-spectrum penicillins | Amoxicillin | Chest, ear, throat, dental |
| Macrolides | Azithromycin | Chest, some STIs; penicillin allergy |
| Quinolones | Ciprofloxacin | Urinary, gut, prostate |
| Sulfonamide combinations | Co-trimoxazole (Durobac) | Urinary, chest, PCP |
See the antibiotics and antimicrobials hub.
What to check before using Doxycycline
Take it sitting or standing upright, with a full glass of water, and stay upright for at least 30 minutes afterwards. Do not take it lying down or immediately before bed. This is the most important practical instruction on this page — it prevents the capsule lodging in the gullet and causing painful ulceration.
Use sun protection. Doxycycline causes marked photosensitivity, and people burn after far less exposure than usual. Sunscreen, a hat and covered arms matter, and this is easily underestimated in a South African summer.
Separate it from dairy, antacids, and iron, zinc, calcium or magnesium supplements by two to three hours. These bind doxycycline and reduce absorption. A small amount of food is fine and reduces nausea.
Finish the whole course.
Tell your prescriber or pharmacist if:
- You are pregnant, planning pregnancy or breastfeeding. Tetracyclines are avoided — they affect developing bones and teeth.
- The medicine is for a child under 8, where it is avoided for the same reason: permanent tooth discolouration.
- You have liver disease.
- You have myasthenia gravis, or lupus.
- You take warfarin, a retinoid such as isotretinoin, methotrexate, or antacids and supplements as above.
- You take the contraceptive pill — vomiting or diarrhoea during a course can reduce its reliability.
- You have a history of oesophageal problems or difficulty swallowing.
Follow the dispensing label. This page does not set doses, and the amount for acne differs from that for an acute infection.
Possible cautions and when to ask a pharmacist or doctor
Oesophageal ulceration is the effect most worth preventing. Pain on swallowing, or pain behind the breastbone after a dose, means stop and seek advice — and review how you are taking it.
Sunburn after minimal exposure is common. Report a severe or blistering reaction.
Nausea and stomach upset are frequent; a little food helps, but avoid taking it with dairy.
Thrush may follow, as with any broad antibiotic.
Diarrhoea. Severe, watery or bloody diarrhoea, particularly with fever and particularly after the course ends, can indicate Clostridioides difficile infection.
For malaria prevention, no tablet is complete protection. Continue bite avoidance — repellent, covered clothing at dusk and dawn, and a treated net — and seek medical attention urgently for any fever during or within months of travel, telling the doctor where you have been.
For acne, give it time — six to twelve weeks — and expect it to be used alongside topical treatment rather than alone.
Seek urgent medical attention for severe pain on swallowing or behind the breastbone; a severe or blistering sunburn reaction; a rash that blisters or peels; facial or throat swelling with difficulty breathing; severe or bloody diarrhoea; yellowing of the skin or eyes; severe headache with visual disturbance; or any fever during or after travel to a malaria area.
Related medicine guides
Frequently asked questions
What is doxycycline used for? Chest infections, acne, sexually transmitted infections, tick bite fever, and malaria prevention.
Why must I stay upright after taking it? A capsule that lodges in the gullet dissolves there and can cause painful ulceration. Take it upright with a full glass of water and stay upright for 30 minutes.
Why do I burn so easily on it? Doxycycline causes marked sun sensitivity. Use sunscreen, cover up and limit exposure — this matters a great deal in South Africa.
Can I take it with milk? Separate it from dairy and from iron, calcium, magnesium or zinc by two to three hours. They bind it and reduce absorption.
How long until it helps my acne? Six to twelve weeks, taken daily alongside topical treatment. Stopping early because nothing has changed is the usual mistake.
How long do I take it for malaria prevention? Start before travel, take it daily throughout, and continue for four weeks after leaving the malaria area.