Does Doryx (doxycycline) cause side effects?

Doryx (doxycycline) is a synthetic (man-made) antibiotic derived from tetracycline used for many different types of infections, including respiratory tract infections due to Hemophilus influenzae, Streptococcus pneumoniae, or Mycoplasma pneumoniae. 

It also is used to treat non-gonococcal urethritis (due to Ureaplasma), Rocky Mountain spotted fever, typhus, chancroid, cholera, brucellosis, anthrax, syphilis, acne, and periodontal disease.

Common side effects of Doryx include

Tetracyclines, such as Doryx, may cause tooth discoloration if used in persons below 8 years of age. Exaggerated sunburn can occur with tetracyclines; therefore, sunlight should be minimized during treatment.

Serious side effects of Doryx include

Drug interactions of Doryx include aluminum, magnesium, or calcium-based antacids, such as Mylanta, Maalox, Tums, or Rolaids because, like food, these medications bind Doryx in the intestine and prevent its absorption.

  • Similarly, Doryx should not be taken with minerals (such as calcium or iron) or with bismuth subsalicylate (Pepto Bismol).
  • Doryx may enhance the activity of warfarin and cause excessive "thinning" of the blood leading to exaggerated bleeding, necessitating a reduction in the dose of warfarin.
  • Phenytoin, carbamazepine, and barbiturates may enhance the metabolism (destruction) of Doryx thus making it less effective.
  • Doryx may interfere with the action of penicillins and should not be combined with penicillins.
  • It may also reduce the effect of oral contraceptives.
  • Combining tetracyclines and methoxyflurane may reduce kidney function. 

Tetracycline antibiotics, such as Doryx, can have toxic effects on development of bone in the fetus. Tetracyclines are not recommended during pregnancy unless there is no other appropriate antibiotic. 

Doryx is secreted into breast milk but the extent of absorption by the breastfed infant is not known. Since tetracyclines can cause toxic effects on bone, the use of tetracyclines in nursing mothers is of concern. 

The physician must decide whether to recommend that a nursing mother discontinue breastfeeding during treatment with Doryx or change to a different antibiotic.

What are the important side effects of Doryx (doxycycline)?

Doxycycline is generally well-tolerated. The most common side effects are

Tetracyclines, such as doxycycline, may cause tooth discoloration if used in persons below 8 years of age. Exaggerated sunburn can occur with tetracyclines; therefore, sunlight should be minimized during treatment.

Doryx (doxycycline) side effects list for healthcare professionals

Clinical Trial Experience

The safety and efficacy of Doryx Tablets, 200 mg as a single daily dose was evaluated in a multicenter, randomized, double-blind, active-controlled study. Doryx Tablets, 200 mg was given orally once-a-day for 7 days and compared to doxycycline hyclate capsules 100 mg given orally twice daily for 7 days for the treatment of men and women with uncomplicated urogenital C. trachomatis infection.

Adverse events in the Safety Population were reported by 99 (40.2%) subjects in the Doryx Tablets, 200 mg treatment group and 132 (53.2%) subjects in the doxycycline hyclate capsules reference treatment group. Most AEs were mild in intensity. The most commonly reported adverse events (Table 1) in both treatment groups were

Table 1: Adverse Reactions Reported in Greater than or Equal to 2% of Subjects

DORYX Tablets, 200 mg
N = 246
Preferred Termn (%)
Subjects with any AE99 (40.2)
  Nausea33 (13.4)
  Vomiting20 (8.1)
  Headache5 (2.0)
  Diarrhea8 (3.3)
  Abdominal Pain Upper5 (2.0)
  Vaginitis Bacterial8 (3.3)
  Vulvovaginal Mycotic Infection5 (2.0)

Because clinical trials are conducted under prescribed conditions, adverse reaction rates observed in the clinical trial may not always reflect the rates observed in practice.

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of doxycycline. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate a causal relationship to drug exposure.

Due to oral doxycycline’s virtually complete absorption, side effects to the lower bowel, particularly diarrhea, have been infrequent. The following adverse reactions have been observed in patients receiving tetracyclines:

  • Anorexia, nausea, vomiting, diarrhea, glossitis, dysphagia, enterocolitis, inflammatory lesions (with monilial overgrowth) in the anogenital region and pancreatitis.
  • Hepatotoxicity has been reported.
  • These reactions have been caused by both the oral and parenteral administration of tetracyclines.
  • Superficial discoloration of the adult permanent dentition, reversible upon drug discontinuation and professional dental cleaning has been reported.
  • Permanent tooth discoloration and enamel hypoplasia may occur with drugs of the tetracycline class when used during tooth development.
  • Esophagitis and esophageal ulcerations have been reported in patients receiving capsule and tablet forms of drugs in the tetracycline- class.
  • Most of these patients took medications immediately before going to bed.
  • Rise in BUN has been reported and is apparently dose-related.
Hypersensitivity Reactions
Intracranial Hypertension

Thyroid Gland Changes

  • When given over prolonged periods, tetracyclines have been reported to produce brown-black microscopic discoloration of thyroid glands.
  • No abnormalities of thyroid function are known to occur.

What drugs interact with Doryx (doxycycline)?

Anticoagulant Drugs

  • Because tetracyclines have been shown to depress plasma prothrombin activity, patients who are on anticoagulant therapy may require downward adjustment of their anticoagulant dosage.


  • Since bacteriostatic drugs may interfere with the bactericidal action of penicillin, it is advisable to avoid giving tetracyclines in conjunction with penicillin.

Antacids And Iron Preparations

  • Absorption of tetracyclines is impaired by antacids containing aluminum, calcium, or magnesium, bismuth subsalicylate, and iron-containing preparations.

Oral Contraceptives

  • Concurrent use of tetracycline may render oral contraceptives less effective.

Barbiturates And Anti-Epileptics

  • Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline.


  • The concurrent use of tetracycline and Penthrane (methoxyflurane) has been reported to result in fatal renal toxicity.

Drug/Laboratory Test Interactions

  • False elevations of urinary catecholamines may occur due to interference with the fluorescence test.

Treatment & Diagnosis

Medications & Supplements

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Medically Reviewed on 12/10/2020
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Professional side effects and drug interactions sections courtesy of the U.S. Food and Drug Administration.