DIY Antihistamines

For pet owners wanting to go it alone and explore the use of over-the-counter medication in their pet, antihistamines are a good place to start.  A broad and diverse family of drugs, their effects range from anti-allergy and cough suppression, through to anti-nausea, and appetite stimulation. Sedation is the most common side effect, which is sometimes exactly what’s desired.  Just like in man, your dog shouldn’t drive nor your cat use heavy machinery when taking antihistamines..


Antihistamines are one of the treatment options for dogs and cats that suffer with atopy (skin, paw and ear problems due to airborne allergens), and are useful in a couple of other situations.  They are of no use for treating contact, flea or food allergies.  Rather than completely eliminating symptoms, these drugs may decrease severity, improve quality of life, and reduce dependency on cortisones and/or cyclosporine.

.They are appealing to many pet owners who:

  • have personal experience of the effectiveness of such drugs  in man;
  • like the over-the-counter availability of many antihistamines in chemists;
  • are dissatisfied with cortisones, and unable to afford cyclosporine or desensitisation.

The downsides:

  • Antihistamines are no cure and, like cortisones and cyclosporine, only suppress allergic reactions. They are only effective in up to 33% of dogs, and up to 73% of cats with atopy, but may not eliminate all itchiness and the need for other treatments.
  • An animal may be responsive to one antihistamine but not another, so a 3-6 week cycle of experimentation is required. By testing at least 3-4 different drugs, pet owners can work-out which agent works best.
  • While this family of drugs is safe enough to be available without script in many cases, they are not without side effects. Described below, they are uncommon, usually mild, and resolve on discontinuation of treatment.

.The antihistamine drug trial protocol for atopy:j

antihistamine trial flowchart


When doing the trial:

  • It is easiest to be confident a drug is effective if the trial is done during the times of year when your pet’s allergies are known to be unrelentingly bad;  if you start treating with a drug and coincidentally the wattle stops flowering, you may be lead to believe the antihistamine worked well.  Spring and summer are usually the worst seasons, but get your vet to check your pet’s medical history for more accurate patterns.
  • To firm-up our certainty an improvement is really a drug effect, it is best to rechallenge: stop the antihistamine after a month of use and watch for the symptoms to return. If they do, you win; if not, back to square-one.
  • Put your dog on an Essential Fatty Acid Supplement or fish-based diet, as such diets seem to make antihistamines more potently effective.
  • If you find a drug that works, continue to try a few more, as others may be even more effective.

lj antihistamine dose rates

.Here is a link to a paper which desribes the use of Telfast, an over-the-counter, once daily antihistamine for atopy in dogs, and it’s effectiveness equivalent to cortisone after 6 weeks of treatment.


Insect bite reactions:

Vets commonly see dogs affected by acute allergic reactions to insect bites (bees, ants, wasps) with symptoms of local swelling and itchiness, often facial,  and lumps or hives erupting suddenly all over the body. Very rarely more dramatic symptoms are collapse, vomiting, breathing difficulty, and heart rhythm disturbances. Vaccination reactions rarely manifest similarly. For more detail, see Insect Bite Reactions: from Itch to Anaphylaxis.

While antihistamines are only really effective when given before exposure to an allergen, they are often given by vets as an injection to treat such reactions. An antihistamine tablet given as first-aid by an owner who cannot get to a veterinarian may be of use, and such advice is often given over the phone by after-hours veterinarians.  If given early, it may slow or limit the progression of the reaction, or at least have some sedative effect,  calming an agitated dog driven mad by their bee sting.


Notes on diphenhydramine:

This drug has a variety of actions, beyond just treating itchy skin, and is worth keeping on hand in your doggy first aid kit. Branded as ‘Benadryl Original Formula’ syrup or Snuzaid® in Australia,  it has mild cough suppressant, sedative and antinausea actions. It’s unpalatable in liquid form and doesn’t really touch-the-sides with severe Kennel Cough, but can be useful for car sickness, mild tracheitis, and acute allergies..

Notes on Periactin® in cats:

This over-the-counter antihistamine for man is often used by vets trying to stimulate appetite in cats. While not wanting to mask loss-of-appetite due to disease, this agent can be useful in cats whose eating habits may have been disrupted by  the stress of hospitalisation, cattery, house guest or other diseases (syntax intended)..

Antidepressant antihistamines:

There are several antihistamines that are also antidepressants and yes, Clomicalm® has the same active as Placil®, a product for man. In these drugs the psychotropic/sedative effects are the desired treatment goals, and the antihistamine effect coincidental.  If lucky you can resolve your terrier’s skin and separation anxiety in one hit..


These depend on which drug is used, and are reported to occur in up to 25% of dogs and 10-40% of cats. Don’t be too put off by these as they are usually mild sedation or tummy upsets, which resolve when treatment is stopped.

  • Drowsiness, which may abate after 3-7 days of use, so do persist if not severe.  Speak with your vet before giving antihistamines to dogs on anti-seizure medication as they may increase sedative side effects.
  • Stimulatory: excitement, vocalising, hunger, or thirst.
  • Gastrointestinal: salivation, vomiting, diarrhoea, off food.
  • Haematologic side effects are rare and detected by blood test if using some agents in the longer-term.
  • Blood pressure and rhythm effects are rare but demand care when using is animals with heart disease, hypertension, glaucoma and hyperthyroidism.
  • Don’t use combination cold and flu medications that also have other ingredients like paracetamol – speak with your pharmacist or vet if confused. Be careful not to confuse Benadryl Original Formula, with other Benadryl combination products.



While all these dose rates are correct as of 2009, I don’t wish to be held responsible for incorrect dose calculations or misuse of this information. If you’re uncertain if your pet is atopic, or your math is poor, you should speak with your vet to make sure the exercise is safe and worthwhile.


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38 Responses to “DIY Antihistamines”

  1. The layout for your web site is a bit off in OmniWeb. Even So I like your website. I may have to install a “normal” browser just to enjoy it. 🙂

  2. Nicoletta says:

    Thanks Matt… yet again your blog has helped me (my dog) so much!

  3. Ben says:

    Hey, my 15 year old cat has diabetes, and I am wondering if it is okay to give her the antihistamine diphenhydramine. we need to relax her so she can get a good brushing/cleaning. If you have any other suggestions on how to calm her for this, we would appreciate hearing them. Thanks in advance!

  4. anthony parker says:

    I would say this is the best website that I’ve seen on this subject. My beloved four-legged human suffers terribly in the spring and summer (I’m in Australia so there’s lots of both) and these do appear to give some relief. Cutting out the dry foods with wheat products, or at least buying only the very best ones seems to have helped too though she still suffers. She is so much more playful during the winter months. Thank you!!!

  5. Lisa says:

    Matt, thank you so much. My darling little Am Staff is allergic to grass, and with a love of playing manically with other dogs, the park is our favourite place. Lilly suffers terribly with itchy skin and paws, and the vet medication is outrageously expensive, and not particularly effective. I have followed your directions, and she is itch free for the first time this summer 🙂 Lilly and I thank you 🙂

  6. Wayne says:

    Ok… After reading your website, I feel that I have confidence in helping my dog with her skin allergies. It’s the dosages that confuse me a little. Help me out here. If I give my dog liquid Benadryl and she weighs 5 kg, does that mean she’ll get the normal dosage on the bottle or is it less?

  7. admin says:

    hi wayne, the dose is 1-4mg/kg three times a day. If we chose a middle of the range dose for your dog say 2mg/kg, then your dog needs: 5kg x 2mg/kg= 10mg. Check the label of your benadryl: if its 100mg/ml then you dog needs a tenth of a ml, ie 0.1ml. If your benadryl is 5mg/ml then your dog needs 2ml. So to answer, the dose depends on the weight of a dog, and the strength of the medication.

  8. sue chakos says:

    Great blog – thanks for this

  9. Jenny says:

    Thank you so much for this, my cat is allergic to her own sweat and loves sitting on radiators, which results in scaly, sore patches followed by hair loss. I have tried some of these and she is now regrowing her coat. Thank you again.

  10. Peter says:

    Very informative article Dr. Matt. Very helpful as well. The dosage table is just what I was looking for. Vet gave me one but I lost it. I have seen diphenhydramine and even cetirizine super cheap at walmart. Can buy 14 tablets of 10mg cetirizine for .88cents at my local walmart! Can get 36 tablets of diphenhydramine for same price. I have a mastiff so it can get expensive. Thanks again!

  11. patricia says:

    I have a Bichon” Frise female, every time have her coat clip she get a skin allegy. what can I put on it

  12. admin says:

    the itch your dog is experiencing may be an allergy to a grooming product, or may not even be an allergy at all. Many dogs become itchy after grooming due to the slight abrasion of the skin by blades and guides, and the irritation of residual clippings left in the coat.

    Many pet owners report this and vets use antibiotics, cortisones, and medicated or emollient shampoos to treat.

    If the itch is all over, it would be impractical to apply anything topically. You could explore the use of antihistamines, but if the mechanism is not allergic, it may not be of benefit.


  13. Amy says:

    Hi there, thanks for sharing this info. I was wondering if you could tell me which corticosteroids can be used in dogs please? In particular, I’d like to know if prednisolone is safe please? Thank-you.

  14. admin says:

    Pretty much all the same corticosteroids that are used in man are used in cats and dogs, so, yes, prednisolone is used in animals.

  15. joe o brien says:

    Matt can you help. My german shepherd cross Layla is two years old and she suffers from ear infections and itchieness and she also licks her paws,it is not that bad as she does not break the skin on her paws.
    I was wondering if an antihistamine would work.She is 20kilo.If so which one would You recommend.

    Thank You.


  16. admin says:

    as stated above, 30% chance it may help, 70% change it wont make a difference. GSDs are also prone to fungal infections which will manifest as paw and ear itchiness, but these req antifungal rx. No specific AH recommended, I usu try chlorphenoramine first.

  17. Mandy brookshaw says:

    Hi, my staffie appears to have an allergy to grass , is it ok to use citirizine for him as he is licking his paws and legs until they bleed, or should I use a steroid , I didn’t really want to use a steroid unless I have to, thanks Mandy

  18. admin says:

    cant say for sure without seeing.

    citrizine is antimicrobial so will only treat secondary bacterial, not the allergy.

    steroid works on allergy.

  19. ceil says:

    Please know we in USA are grateful for your info – poor Martie (bulldog ancestry) was having another “episode” and Benedryl was causing excitability. Martie is on his 2nd day with chorphenoramine and his scratching has decreased 85-90% at this point despite the moderate and high pollen counts! We aplaud Aussies! You are wonderful, Dr. Matt!

  20. Carole says:

    there is a new antihistamine called prevalin applied as a nose spray could it be used
    on dogs do you know my dog responds well with the pills but is very drowsy. thanks Carole

  21. schip mom says:

    My 2 year old schipperke was diagnosed with allergies in April and had a cough that sounded like kennel cough, it was not kennel cough. The vet gave him Temaril P and he cleared up. The cough is back, what can I give him to remedy the situation. I do have some liquid prednisone to add to an antihistamine but what kind? Would a claratin generic work in combination with the prednisone to equate the temaril P? Thanks, Julaine

  22. admin says:

    Hi Julaine, you are describing proprietary names of products that aren’t the same in Australia. Cough is too nonspecific for me to confidently comment on treatment. I’d talk with your vet. Ask your vet about using asthma puffers for inflammatory airway disease.

  23. artemis says:

    hello! may name is stelios and i have a 2.5 year old female doberman! after 6 7 months of age she start having skin problems. we have try everything until now! she is negative too demodex or scabies. when i gine her antibiotick she is ok but then come back after i stop it. i realise that when i give her a spot on (i try almost everything) she gets well! but last only 2 weeks. the conclusion i made after a lot of visits too vets and tries i that she had flies alergy dermatitis. please help me with my problem. i can find a solution.. ps glucocorticoid work very bad on her! she have fever after used it and the problems with the skin get worse! please help us! thank you!

  24. artemis says:

    hi is me again! i forgot too tell you that we live in a apartment. and my we have constant contact with other dogs(puppies also). she love too play outside! colars dont work on her! spot on just for a few days depents of what i will use! i clean i vacum try too eliminate but with no results! i spot on 2 3 times a month. before 2 3 weeks she got skin anafilaxis but after i give her spot on after 2 days was ok. i see her get well for a few days and then goes from well too very bad! i want her too be well all year! no problem with the cost! just too be ok! and the last thing i want too ask you. can we male a compination of spot on and antihistamines?
    thank you!

  25. admin says:

    your problem is complex, and you will need to pay somebody local to spend the time fully understanding the medical history, examining your pet, and arriving at the best solution. good luck.

  26. artemis says:

    i paid a lot and too a lot of vets. no one can find a solution. thanks a lot for your help

  27. artemis says:

    not a problem with the money i just cant find anyone who can help me. i gave 500 eu only for convinia. if you can help me just name it

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  29. Lin says:

    This allergy merry-go-round is so frustrating. My 8yo (rescue) Wheaten terrier seems to get temporary relief from Temaril p but I am reluctant to keep him on it indefinitely. We have been to the vet so many times because his licks between his toes to the point of limping. No issues with ears. I have tried different diets. One new protein, raw, home cooked but he still licks. He is also anxious and we have also wondered about stress, but he does stop licking on Tem P. We have used clomipramine and a couple of products suggested by a veterinary behaviourist with no relief. The behaviourist suggested Prozac but I don’t think it is the solution to the foot licking. Is the temeril p the solution or could I try something else?

  30. admin says:

    Prozac is only indicated if we think there is some psychological dimension to the condition. If you can resolve the itch with Temeril P predisone/antihistamine combination, albeit temporarily, then i would contend the dog is licking the paws due to itchiness, not just some sort of OCD or anxiety.

    I’d be surprised if Prozac will help. I’d ensure good Omega 3/6 balance, use Temperil as required. Speak to your vet about poss ketoconazole trial to rule out interdigital malasezzia, and consider atopica if steroid side effects become a problem.

  31. Tristan says:

    If your dog is having itchy allergies, consider putting him on a natural diet, real food, real meat, real veg, no processed dog food. My dog went from horrible itching to happy when I started feeding him raw chicken with bones (it’s the COOKED bones that are dangerous) and tasty veggies. When i felt he wasn’t getting enough bones, I sometimes gave him the same calcium and minerals supplement I take. The vet said I may have added years onto my sweet doggie’s life by giving him real food. AVOID corn, wheat, soy, and sorghum.

    I did end up letting my dog eat soy, but he had no bad reaction to it. Corn seemed to be the culprit. It is the major ingredient in a lot of dog foods. You can look up the BARF (Bones and raw food) diet on line and find out a lot of other things about feeding your dog well.

  32. Claire Henry says:

    Hello….hope you can help. My 6yr Old Exotic was operated on for having a suspected grass seed up his nose….symptoms included sneezing, wheeziness, increase in thirst. Nothing was found (except a massive hole in my bank balance!) and his condition settled after a couple of steroid injections. This spring I have noticed a return of the very same symptoms and was wondering if it could be the onset of hay fever. My son has the same and finds a daily dose of antihistamines helps so… there anything SAFE that I could administer to my poor cat to give relief? I am situated in the UK so no doubt some of the veterinary products available across the pond will not be on sale OTC here but can I give reduced dosage of human medicines safely? Thank you

  33. admin says:

    I dont live in UK either, so cant comment on brands or OTC availability. Print out the table above and take it to you chemist

  34. armina says:

    hi Matt please help me as i have tried everything and constant vet visits…. i have a silky maltese terrior she is 11 this year,very bubbly active dog people still think she is 2… every year around summer in sydney she would get itchy skin which the vet said its an allergy and gave her a shot and after few weeks she would be fine.this year in january same thing happened only she is still suffering and itching and has given herself bold patches the sores seem all ok until she eats at it.5 months almost she is still itchy….she is a house dog so she tip toes on grass for weeing ect and runs inside always kept very clean well groomed and loved to death only now its been 3months she wont let me touch her or go near her,soon as i do she bolts under any bed and wont come out,i am so unhappy i love her to death and now she wont come near me,goes to everyone else in family but me,i have trouble when i try and bath her i cant touch her lower back or back legs she screams and wants to bite me…she is in pain and scared of me cause ive done so much to her and for her,i have tried everything i dont know what do do anymore when i go to vet he says she has allergy to insect bites and gives us antibiotics and tables for itch not helping its been too long something is not right ….please help im going insane missing my dog,she sits 4 meters away opposite me and stares with sad eyes soon as i move she runs..please help me

  35. Debbie says:

    My dog suffers from Marcel tumours and as a side affect she constantly nips the skin on her front legs as they are itchy. The skin is not broken but is now discoloured. Would giving her an antihistamine help? If so, could we use piriton? She is a 15kg springer spaniel.

  36. Cristal says:

    My mechanic has a pit bull that was recently bitten by a spider and his face swelled. Is there anything over the counter that I can give him to bring the swelling down?? at least until he is able to take it to the vet?

  37. Tina says:

    Hi can you please help me my dog has flea allergy dermatitis the vets have told me this he went in had a corterzone injection and was also put on steroids he finished his last lot and was then put on piriton 2xday the piriton doesn’t seem to have any effect so I want to try Benedryl he weighs 10kg im not user how much im supposed to give him , is there anything else out there that can stop my little dog itching he constantly has to have a cone on to stop him chewing himself I would take him back to he vets but ive been there done that and still in the same situation

  38. admin says:

    The antihistamines you are trialling usually have little to no effect on FAD, but they are the last option for vets and pet owners when steroids aren’t desirable, for what ever reason.

    The only hope i can offer you, is that fleas are curable. It just takes time, really good products, treating all animals, and avoiding social contact. Depending on your climate, you may have to give monthly products all year round.

    A dog with flea allergy can chew a single bite for up to 3 weeks. Once youre over this current bout, and it settles, you should view any future recurring itch in the ‘FAD zone’ as an emergency, where you have act immediately – cranking up flea control, identifying where picked up, and possibly a month of cortisone when its at its worst, if you cant prevent reinfestations.

    it could be worse eg airborne

    good luck

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