Drugs (including antibiotics) that block DAO enzymes

Many drugs inhibit diamine oxidase (DAO), the enzyme that degrades histamine​1​. With long-term use of these drugs, exacerbations or further problems may develop with histamine intolerance/overload, including vulvovaginal and urinary tract symptoms.

If you are on any of these drugs over the long-term, including some antibiotics, a rethink may be in order if there is evidence or symptoms of histamine overload. If you’re on a drug regime that ensures some drug is always in your system, the impacts of DAO blocking could also be always at play.

If you only take these drugs once a day or occasionally, the impact is far less, since the drug is out of your system at some stage, allowing DAO to once again degrade histamine. It may slow your histamine clearance, rather than blocking it completely.

The DAO enzyme is essential to eliminate histamine from cells. Without DAO, histamine builds up and can result in symptoms.

Drugs that block DAO

  • Painkillers with metamizol (Dipyrone), acetyl salicylic acid (aspirin)
  • Antihistamines with diphenhydramine (Tylenol, Advil, Benadryl, Dimetapp and others), cimetidina (Tagamet), promethazine (Phenergen, Promacot)
  • Anti-arrhythmics with propafenone (Rythmol) or quinidine (Nuedexta)
  • Anti-asthmatics with theophylline (Theo 24, Theochron, Elixophyllin, aminophylline, and Uniphyl)
  • Antidepressants with amitriptyline (Elavil) or tranylcypromine (Parnate)
  • Antihypertensives with dihydralazine (Adelphane) or verapamil (Isoptin, Calan, Covera, Verap, Verapamil, Verelan)
  • Antirheumatics with acemetacin (many – check the label of your brand)
  • Antiseptic with acriflavine (many – check the label on yours)
  • Antituberulosis with isoniazid (Nydrazid)
  • Bronchiolitics with aminophylline (many – check the label on yours)
  • Cardiotonics with dobutamine (Dobutrex)
  • Diuretics with amiloride (Midamor) and furosemide (Frusemix,, Uremide, Urex, Lasix)
  • Expectorants with ambroxol (Mucosan, many – check the label on yours)
  • Mucolytics with N-acetylcysteine (NAC) (Fluimicil, Frenacil)
  • Antimalarials with chloroquine (Aralen Phosphate) (chloroquine blocks DAO by over 90 per cent)​2​
  • Antibiotics with clavulanic acid (Augmentin, Amoxiplus, Amoxycillan, Acidum Clavulanicum, Clavulansäure, acide clavulanique/clavulanico, Clavulanate Potassium, Kalii clavulanas, etc.) isoniazid (Nydrazid) and quinoline (Levoflaxin​3​ and Levaquin)
  • Antiemetics and prokinetics with metoclopramide (Primperan,  Reglan, Maxolon, Gimoti, Metozolv ODT)
  • Neuroleptics with haloperidol (Haldol, Haldol Decanoate, Haloperidol LA, and Peridol)
  • Tranquilizers with diazepam (Valium, Ducene, Antenex and Propam)
  • Muscle relaxants with pacerone (Amiodarone)
  • Immune modulators (Humira, Enbrel, Plaquenil)


International Society of DAO Deficiency

  1. 1.
    Maintz L, Novak N. Histamine and histamine intolerance. The American Journal of Clinical Nutrition. Published online May 1, 2007:1185-1196. doi:10.1093/ajcn/85.5.1185
  2. 2.
    Leitner R, Zoernpfenning E, Missbichler A. Evaluation of the inhibitory effect of various drugs / active ingredients on the activity of human diamine oxidase            in vitro. Clinical and Translational Allergy. Published online July 18, 2014. doi:10.1186/2045-7022-4-s3-p23
  3. 3.
    Mori K, Maru C, Takasuna K, Furuhama K. Mechanism of histamine release induced by levofloxacin, a fluoroquinolone antibacterial agent. European Journal of Pharmacology. Published online April 2000:51-55. doi:10.1016/s0014-2999(00)00147-3

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Jessica Lloyd - Vulvovaginal Specialist Naturopathic Practitioner, BHSc(N)

Jessica is a degree-qualified naturopath (BHSc) specialising in vulvovaginal health and disease, based in Melbourne, Australia.

Jessica is the owner and lead naturopath of My Vagina, and is a member of the:

  • International Society for the Study of Vulvovaginal Disease (ISSVD)
  • International Society for the Study of Women's Sexual Health (ISSWSH)
  • National Vulvodynia Association (NVA) Australia
  • New Zealand Vulvovaginal Society (ANZVS)
  • Australian Traditional Medicine Society (ATMS)