Weight-based dosing reference for common OTC supplements and medications used in dogs and cats. For educational reference only.
About These Medications
Benadryl (Diphenhydramine)
Diphenhydramine (the active ingredient in original Benadryl) is one of the few over-the-counter antihistamines considered relatively safe for dogs at appropriate doses. It's commonly used for mild allergic reactions, insect stings, motion sickness, and mild anxiety. The standard dose is 1 mg per pound of body weight, up to a maximum of 50 mg per dose, given every 8–12 hours.
Critical warning: Only use products containing plain diphenhydramine. Many Benadryl formulas include decongestants (pseudoephedrine), xylitol, or alcohol — all of which are toxic to dogs. Read every ingredient. For cats, diphenhydramine can cause paradoxical excitation and should only be given under veterinary guidance.
Melatonin
Melatonin is a naturally occurring hormone that regulates sleep-wake cycles. It is sometimes used in dogs for anxiety (thunderstorms, fireworks), hair loss (alopecia X), or sleep disturbances in senior dogs. Typical doses range from 1.5 mg for small dogs to 6 mg for large dogs, given 30–60 minutes before the stressful event.
Critical warning: Many melatonin products for humans contain xylitol as a sweetener — xylitol is severely toxic to dogs and can cause fatal hypoglycemia and liver failure. Always check the label for xylitol before giving melatonin to your pet. Use only xylitol-free formulations.
Fish Oil (Omega-3 Fatty Acids)
Omega-3 fish oil is one of the most evidence-backed supplements in veterinary medicine, with demonstrated benefits for skin and coat health, joint inflammation (particularly useful in dogs with arthritis), cardiovascular health, and cognitive function. The active components are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) — these are what you're dosing, not the total fish oil volume.
The general target is approximately 100 mg of combined EPA+DHA per kilogram of body weight per day for general health. Higher doses (up to 300 mg/kg) may be recommended by vets for specific conditions like hyperlipidemia or severe arthritis, but only under supervision.
Frequently Asked Questions
Can I give my dog Benadryl for allergies?
Plain diphenhydramine (original Benadryl, not multi-symptom formulas) can help with mild environmental allergies or allergic reactions in dogs. It won't treat the underlying allergy, and many dogs experience drowsiness. For chronic allergy management, veterinary-prescribed antihistamines like cetirizine or medications like Apoquel or Cytopoint are more effective.
Is xylitol dangerous to dogs?
Extremely. Xylitol triggers a massive insulin release in dogs, causing life-threatening hypoglycemia within 10–60 minutes. It can also cause acute liver failure. Even small amounts can be fatal. Check all human products — gum, candy, peanut butter, melatonin, vitamins — before giving them to your dog.
Can cats take fish oil?
Yes, fish oil is generally safe for cats and may benefit skin, coat, and kidney health. Cats are obligate carnivores and can use EPA/DHA directly. However, excessive amounts can interfere with blood clotting or cause GI upset. Start low and increase gradually with vet guidance.
What should I do if my pet is having a severe reaction?
Signs of anaphylaxis in pets: facial swelling, difficulty breathing, collapse, pale/white gums, vomiting, diarrhea. This is a life-threatening emergency — go to an emergency vet immediately. Do not wait. ASPCA Poison Control: (888) 426-4435.
Why doesn't this calculator cover prescription medications?
Prescription medications have complex dosing requirements that vary by individual health status, drug interactions, organ function, and diagnosis. Providing dosing estimates for prescription medications without veterinary oversight would be dangerous. Always follow your vet's specific instructions for prescription drugs.
Sources: Plumb's Veterinary Drug Handbook (10th ed.); Merck Veterinary Manual — Drug Dosages; ASPCA Animal Poison Control Center; Bauer (2011) "Therapeutic use of fish oils in companion animals" — JAVMA; WSAVA Global Pain Council.