Doxycycline 100 mg Capsules: Prescription Tetracycline Antibiotic for Respiratory Infections, Acne, Lyme Disease & Chlamydia

Information last reviewed: May 2026 — for educational purposes only.

Doxycycline is a second-generation tetracycline antibiotic with broad-spectrum bacteriostatic activity. It is one of the most versatile antibiotics in clinical medicine, used to treat community-acquired pneumonia (including atypical organisms such as Mycoplasma pneumoniae and Chlamydophila pneumoniae), inflammatory and non-inflammatory acne vulgaris, Lyme disease (early and late stages), pelvic inflammatory disease (PID), chlamydial urethritis and cervicitis, malaria prophylaxis for travellers, rosacea, and rickettsial infections. It is prescription-only in all major markets.

What Is Doxycycline?

Doxycycline inhibits bacterial protein synthesis by binding reversibly to the 30S ribosomal subunit, blocking aminoacyl-tRNA from attaching to the ribosome-mRNA complex. Without functioning ribosomes, bacteria cannot produce essential proteins and growth is arrested (bacteriostatic). Its broad spectrum covers both Gram-positive and Gram-negative bacteria, as well as intracellular pathogens such as Chlamydia, Rickettsia, and Mycoplasma — organisms that beta-lactam antibiotics like penicillin cannot reach because they lack cell walls.

Two main salt forms are used: doxycycline hyclate (more commonly used in the US, slightly more irritating to the oesophagus when taken dry) and doxycycline monohydrate (considered gentler on the stomach and oesophagus). Both are clinically equivalent in terms of antimicrobial activity.

Is Doxycycline Available Over the Counter?

Doxycycline is prescription-only in the US, UK, Canada, EU, and Australia. It cannot be purchased without a valid prescription at a licensed pharmacy in these jurisdictions. Telehealth services can prescribe doxycycline for common indications including acne, chlamydia, and Lyme disease based on clinical assessment.

Capsule and Tablet Strengths

• 50 mg capsules — used primarily for long-term acne treatment and rosacea maintenance; lower dose reduces GI side effects
• 100 mg capsules / tablets — the standard dose for most infections; typically taken once or twice daily
• Periostat (20 mg tablets) — sub-antimicrobial dose used adjunctively in periodontal disease
• Oracea (40 mg delayed-release capsules) — US brand specifically licensed for inflammatory rosacea
• Vibramycin (syrup 25 mg/5 ml) — liquid form for children and those who cannot swallow capsules

Standard dosing for most infections is 100 mg twice daily or 200 mg once daily for 7–14 days. Doxycycline should be taken with a full glass of water and the patient should remain upright for at least 30 minutes afterwards to prevent oesophageal ulceration. It can be taken with food to reduce GI upset, unlike some tetracyclines. Avoid within 2 hours of antacids, calcium, or iron.

Price of Generic Doxycycline

Generic doxycycline 100 mg is among the least expensive prescription antibiotics. A 14-day course typically costs only a few dollars with a pharmacy discount card in the US. Hyclate and monohydrate generics are widely available at similar prices. Brand-name Vibramycin is rarely dispensed.

Frequently Asked Questions

Can I take doxycycline with dairy or milk?

Unlike older tetracyclines, doxycycline absorption is only minimally affected by dairy products and food — so it can generally be taken with food to reduce stomach upset. However, antacids, calcium supplements, and iron significantly reduce absorption and should be spaced at least 2 hours apart.

Can doxycycline treat a UTI?

Doxycycline is not a first-line antibiotic for uncomplicated urinary tract infections because it achieves lower urinary concentrations than antibiotics like nitrofurantoin, trimethoprim, or ciprofloxacin. It may be used for chlamydial urethritis (sometimes confused with UTI) or UTI caused by specific susceptible organisms, but only when directed by a prescriber.

Does doxycycline cause sun sensitivity?

Yes. Doxycycline and all tetracyclines can cause photosensitivity (increased sunburn susceptibility). Patients should apply broad-spectrum sunscreen, wear protective clothing, and limit prolonged sun exposure during treatment and for several days after completing the course.

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