Demeclocycline (INN, BAN, USAN, brand name Declomycin) is a tetracycline antibiotic which was derived from a mutant strain of Streptomyces aureofaciens.

[8][9] It is widely used (though off-label in many countries including the United States) in the treatment of hyponatremia (low blood sodium concentration) due to the syndrome of inappropriate antidiuretic hormone (SIADH) when fluid restriction alone has been ineffective.

[11] The use in SIADH actually relies on a side effect; demeclocycline induces nephrogenic diabetes insipidus (dehydration due to the inability to concentrate urine).

[17] Tetracyclines bind to cations, such as calcium, iron (when given orally), and magnesium, rendering them insoluble and nonadsorbable for the gastrointestinal tract.

[20] Brand names include Declomycin, Declostatin, Ledermycin, Bioterciclin, Deganol, Deteclo, Detravis, Meciclin, Mexocine, and Clortetrin.