Dimenhydrinate
Diphenhydramine teoclate (8-chlorotheophylline and diphenhydramine complex)
Also known as: Dramamine · Gravol · Dimetabs · Triptone · Dinate · Dramanate · Dymenate · chloranautine · dimenhydrinatum · diphenhydramine teoclate · diphenhydramine theoclate
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Prevention and treatment of motion sickness (antiemetic) | 4-8 mg/kg | PO | three times daily | — | 🌎 NA |
| Prevention and treatment of motion sickness | 4-8 mg/kg | PO | q8h | — | 🌎 NA |
| Antihistamine | 4-8 mg/kg | PO | q8-12h | — | 🌎 NA |
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Prevention and treatment of motion sickness/vomiting | 8 mg/kg | PO | q8h | — | 🌎 NA |
| Prevention and treatment of motion sickness/vomiting | 4-8 mg/kg | PO | q8h | — | 🌎 NA |
| Antihistamine | 4 mg per cat | PO | q8h | — | 🌎 NA |
| Adjunctive treatment of pancreatitis | 8 mg/kg | PO | q8h | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Dimenhydrinate is a first-generation H1-receptor antagonist widely known by the human brand name Dramamine®. It is an ethanolamine derivative consisting of a salt complex of diphenhydramine (approx. 54%) and 8-chlorotheophylline (approx. 46%), a mild stimulant added to counteract the sedative effects of the antihistamine.
In veterinary medicine, it is primarily utilized for its antiemetic properties to prevent and treat motion sickness in dogs and cats.
Clinical Pearls:
- Because histamine is not considered a primary mediator of vomiting in cats, other antiemetics (e.g., maropitant, prochlorperazine) may be more efficacious for feline motion sickness.
- It is often considered "half-strength diphenhydramine" and can be used whenever an H1-blocker is indicated.
- It may be used as an adjunctive treatment for feline pancreatitis to reduce histamine-mediated microvascular permeability.
Mechanism of action
Dimenhydrinate exhibits antihistaminic (H1), antiemetic, anticholinergic, CNS depressant, and local anesthetic effects, primarily driven by the diphenhydramine moiety.
- H1-Receptor Antagonism: Competitively blocks histamine at H1 receptors → prevents histamine-mediated responses in the GI tract, blood vessels, and respiratory tract.
- Antiemetic/Vestibular Effect: Blocks muscarinic acetylcholine receptors → inhibits acetylcholine stimulation of the vestibular and reticular systems → reduces motion sickness.
- Pancreatitis Application: H1 blockade → reduces histamine-mediated increases in microvasculature permeability → potentially limits hemorrhagic necrosis in feline pancreatitis.
Safety & warnings
Contraindications
- Hypersensitivity to dimenhydrinate or other antihistamines in its class
- Angle closure glaucoma (use with caution)
- Prostatic hypertrophy (use with caution)
- Pyloroduodenal or bladder neck obstruction (use with caution)
- COPD if mucosal secretions are a problem (use with caution)
- Hyperthyroidism, seizure disorders, cardiovascular disease, or hypertension (use with caution)
Adverse effects
- CNS depression (lethargy, somnolence)
- Anticholinergic effects (dry mouth, urinary retention)
- GI effects (diarrhea, vomiting, anorexia - less common)
Precautions
Working Dogs: The sedative effects of antihistamines may adversely affect the performance of working dogs.
Allergy Testing: Antihistamines can decrease the wheal and flare response to antigen skin testing. Discontinue at least 4 days before testing.
- Tolerance to the CNS depressant effects can ensue after a few days of therapy, and antiemetic effectiveness may also diminish with prolonged use.
- Safe for use during pregnancy if used cautiously (FDA Category B in humans; Papich Class B in veterinary). Small amounts are excreted in milk but are unlikely to pose much risk to nursing offspring.
Drug interactions
May potentiate the anticholinergic effects of other anticholinergic drugs.
Increased sedation can occur if combined with other CNS depressants.
May mask the clinical signs of ototoxicity; use with caution when administering concomitantly.
Monitoring
- Clinical efficacy (reduction in vomiting/motion sickness)
- Adverse effects (sedation, anticholinergic signs such as dry mouth or urinary retention)
Pharmacokinetics
Absorption
Well absorbed after oral administration. Antiemetic effects occur within 30 minutes of PO administration. Antiemetic effects occur almost immediately after IV injection. Duration of effect is usually 3-6 hours.
Distribution
Small amounts are excreted in milk. Crosses the blood-brain barrier.
Metabolism
Diphenhydramine is metabolized in the liver.
Elimination
The majority of the drug is excreted as metabolites into the urine.
Overdose
Overdosage may cause CNS stimulation (excitement to seizures) or depression (lethargy to coma), anticholinergic effects, respiratory depression, and death.
Treatment:
- Empty the gut if ingestion was oral. Induce emesis if the patient is alert and CNS status is stable.
- Administration of a saline cathartic and/or activated charcoal may be given after emesis or gastric lavage.
- Symptomatic and supportive therapies.
- Phenytoin (IV) is recommended in the treatment of seizures caused by antihistamine overdose in humans; use of barbiturates and diazepam are avoided.
Available products
Formulations
- Oral tablets
- Chewable tablets
- Oral liquid/suspension
- Injection
Human-labeled
- Dimenhydrinate Oral Tablets: 50 mg (regular & chewable) (Dramamine®, Dimetabs®, Triptone®)
- Dimenhydrinate Oral Liquid: 12.5 mg/4 mL, 12.5 mg/5 mL, 15.62 mg/5 mL (Dramamine®, Children's Dramamine®)
- Dimenhydrinate Injection: 50 mg/mL in 1 mL and 10 mL vials (Dinate®, Dramanate®, Dymenate®)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at room temperature; avoid freezing the oral solution and injectable products. Oral solution should be stored in tight containers; tablets stored in well-closed containers.
Client information
Travel Tip: For motion sickness, administer the medication 30 to 60 minutes before travel begins for the best effect.
- Sedation: This medication commonly causes drowsiness and lethargy. Ensure your pet is in a safe environment.
- Dry Mouth: Your pet may experience a dry mouth; ensure fresh water is always available.
- Human Products: Do not use human combination cold or allergy products (which may contain decongestants or pain relievers like acetaminophen) as these can be highly toxic to pets. Only use the exact product recommended by your veterinarian.
- Contact your veterinarian if you notice severe agitation, seizures, or difficulty urinating.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.