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Doxycycline is a tetracycline antibiotic and a preferred treatment for many uncomplicated chlamydia infections. A test result, the site of infection and pregnancy status can all change the plan a doctor sets.

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What is doxycycline 100mg?

Doxycycline is taken as a capsule or tablet, often twice daily for chlamydia. The indication, regimen and follow-up depend on your history and country guidance — a licensed doctor decides whether it is appropriate, and prescribing is never automatic.
Active ingredient: doxycycline. Dosage: 100 mg.

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How it works

Doxycycline binds to the 30S subunit of the bacterial ribosome and blocks aminoacyl-tRNA from entering the A-site. This halts peptide chain elongation, stopping protein synthesis and preventing the bacteria from replicating. (Nguyen et al., Biol Chem 2014, PMID 24497223)

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Trial evidence for chlamydia

The key comparative trial (Geisler et al., N Engl J Med 2015, PMID 26699167; NCT00980148) was an open-label, randomised non-inferiority study conducted in youth correctional facilities in the United States, where directly observed therapy was feasible. A total of 567 adolescents with urogenital Chlamydia trachomatis infection were randomly assigned to azithromycin 1 g as a single dose or doxycycline 100 mg twice daily for 7 days. The primary endpoint was treatment failure at 28 days, determined by nucleic acid amplification testing, sexual history and OmpA genotyping. There were zero treatment failures in the doxycycline group (0%) and five in the azithromycin group (3.2%); non-inferiority of azithromycin was not established. The trial did not assess rectal or pharyngeal infection, and the results may not generalise to settings where adherence is not directly observed.

Evidence-based first option

Commonly recommended for uncomplicated chlamydia when no contraindication applies.

Covers infection sites

The clinician checks genital, rectal and throat exposure so testing and follow-up fit the case.

Partner advice included

Paired with advice on abstinence, partner notification and repeat testing when needed.

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Dosing

A common uncomplicated-chlamydia regimen is 100 mg twice daily for seven days. The diagnosis and local guidance determine the final course.
1

Before treatment

Confirm testing and pregnancy status.
2

Days 1–7

Take the prescribed doses evenly, twice a day.
3

Afterwards

Follow partner and sexual-contact advice.

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What has been reported

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Who it is not suitable for

  • Pregnancy, because doxycycline crosses the placenta and can bind to calcium in developing bone and teeth, causing permanent tooth discolouration and reversible skeletal growth delay in the foetus
  • A tetracycline allergy
  • A relevant interacting medicine: divalent and trivalent cations (calcium, iron, magnesium, aluminium, zinc) chelate doxycycline in the gut, forming insoluble complexes that reduce absorption — the reason for the separation advised in the dosing instructions
For severe, sudden or unexpected symptoms, call your local emergency number or go to the nearest emergency department, then let your doctor know through your account chat.

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How to take it

Swallow with a full glass of water while sitting or standing, and do not lie down for at least 30 minutes. Separate antacids and supplements containing iron, calcium, magnesium, aluminium or zinc as your pharmacist advises. Take every dose and finish the course even if symptoms settle. If a dose is missed, take it when remembered unless the next is near — do not double up.
  • Severe pelvic or testicular pain, fever, vomiting, pregnancy, eye symptoms after exposure, or feeling acutely unwell
  • A severe allergic or skin reaction, severe headache with visual change, painful swallowing, or severe or bloody diarrhoea
  • A dose was missed repeatedly, sex occurred before the advised interval, a partner was not treated, or symptoms persist
Keep in the original package, away from moisture and direct heat, and out of children’s reach. Follow the temperature limit on your pack and do not use it after the expiry date.

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How Hi-Doctor handles it

An EU-licensed doctor reads your questionnaire and answers within 24 hours. If the doctor decides it is not safe to prescribe, the consultation fee is refunded in full. Follow-up happens in the private chat inside your account, under GDPR — no WhatsApp, no SMS. For the full walkthrough of a prescribed course, see the doxycycline chlamydia guide. Related: azithromycin, the alternative when doxycycline is unsuitable. See also how a Hi-Doctor consultation works, safety and eligibility checks, and pricing.

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Start a consultation

Sexual health consultation

Answer the sexual health questionnaire and a registered doctor reviews it. They decide whether treatment is appropriate, which one, and at what dose — and declining is a normal outcome. See what it costs and how the review works.
This page is reference information, not medical advice and not a prescription. Whether a medicine is appropriate for you is decided by a registered doctor after reviewing your consultation.