Henry had taken Benadryl before without any problems.
Then one Saturday morning, everything changed. Within minutes, he was struggling to breathe, and I was racing 20 miles to the nearest emergency vet while wondering if he would survive the drive.
Benadryl is commonly recommended by veterinarians for certain situations, and many dogs tolerate it well. But my experience taught me that even medications a dog has taken before aren’t completely risk-free.
I didn’t know about the side effects of Benadryl for Dogs until Henry’s severe reaction. This article will cover the side effects and what to look for if you suspect a negative reaction.
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Budget Tip: Saving money on your dog's care doesn't always mean choosing the cheapest option. Sometimes it's simply paying close attention. Even if your dog has taken the same medication dozens of times, continue watching them after every dose. Catching a problem early could save both your dog's life and a very expensive emergency vet visit.
What is Benadryl For Dogs Used to Treat?
While the medical name for Benadryl is Diphenhydramine, it’s a basic antihistamine. It can help suppress the symptoms of allergies. My dog Henry’s vet prescribed Benadryl about five years ago.
I had given him 1/2 of a 25 mg pill periodically as his eyes became red, itchy, or gooey. This was more of an issue after he was attacked by a couple of large dogs a few years ago and nearly lost one eye. As part of that attack, his tear duct was crushed in his left eye. Thus, he isn’t as able to flush out foreign objects.
Basically, Benadryl for dogs works the same as it does for humans. It can treat a multitude of mild allergies by providing temporary relief. These allergy symptoms can include:
- Seasonal allergies
- Insect bite
- Skin allergies
- Itchy skin (due to mild allergies)
- Watery eyes (which is what I used it for, Henry)
- Environmental allergies
Does Benadryl Work For Dog Allergies?
It will depend on your dog. Henry’s allergies always seemed to improve each time I gave him a dose. Although I never gave it to him very often. Maybe once every 3 months, and then he’d get a dose once a day for about 3 days. Generally speaking, within that timeframe he’d be back to his normal self. He’s been almost like clockwork.
Could My Dog do Well With Benadryl and Then Suddenly Develop Side Effects?
Yes! This is what happened to Henry, and the severe allergic reaction or side effects that hit him came on very suddenly. They were very scary!
How Much Benadryl Can Dogs Take Safely?
Vets base the amount of Benadryl they prescribe on the weight of a dog. The formula used to calculate the amount of Benadryl is typically 0.9 to 1.8 mg for each pound of a dog’s weight.
Since Henry weighs 13.8 pounds, his vet suggested I give him 1/2 of a 25 mg Benadryl 1-2x/day as needed. However, I would only give him 1/2 once a day as needed. I never wanted to take the chance of overdosing him. Plus, he always seemed to do well on this lower amount.
Frustrated with your vet? Here’s an article on the 15 Red Flags when it’s time to get a new vet.
Even when Benadryl for dogs is given at the correct dose recommended by a veterinarian, unexpected side effects can still occur in rare cases.
Is There a Best Time to Give Benadryl to My Dog?
Generally, vets will say to administer Benadryl to your dog as symptoms dictate. Your vet will know the correct dosage for your dog and how often you will want to give it to your pup. That could mean your dog’s symptoms require treatment on the weekend or after hours.
But, after my experience recently with Henry, my thoughts have changed a bit. Now, I would personally recommend always giving such a drug when you can easily get your dog to veterinary care if it’s required. This may mean treating your dog early in the morning and during the week. I would try to avoid the weekends and late nights if at all possible.
What are the Potential Side Effects of Benadryl for Dogs?
Your dog may have any number of potential side effects from Benadryl. Or your dog may not have any side effect symptoms from the medication. However, you will want to look for these potential side effects:
- Drowsiness (which often is seen as a good thing to calm a dog. I’ve never used it hoping for a sleepy reaction)
- Lethargy
- Unwilling to drink
- No appetite
- Vomiting
Or there could be a severe allergic reaction, which is what happened to Henry.
Within 15 minutes of giving Henry a dose of Benadryl, he suddenly was experiencing symptoms with
- Walking
- Sitting
- Falling over
- Breathing difficulty
That’s exactly what happened to Henry after taking Benadryl for dogs he’d tolerated for years.
It was very scary!
What Should I Do if My Pup Has a Sudden Severe Allergic Reaction to Benadryl for Dogs?
When Henry suddenly had this reaction to Benadryl, it took me by surprise. As I looked at him and called his veterinary medicine clinic, he was getting worse with each passing minute.
His vet was in surgery for at least 2 more hours. I was unwilling to wait since his symptoms were progressing so quickly. So, I called his first emergency vet (he has two) and was put on hold. With no time to wait, I grabbed Henry and rushed to his second emergency veterinary clinic 20 minutes away.
The drive to the emergency vet…
While a family member drove, I called the vet clinic. They said to rush in, which was also a no-brainer.
As we drove, I kept reaching around and putting my hands on Henry. I couldn’t feel any breathing. I patted him and said, “Breathe, Henry! Breathe, baby!” That seemed to bring a very small breath to his little body.
It was one of the scariest drives of my life.
Arriving at the vet clinic…
We arrived at the vet clinic. Henry looked up, and I carried him into the waiting room.
A vet tech came out within minutes and evaluated Henry.
With this evaluation, Henry was moved up to a “same day” vet appointment rather than an emergency appointment. This saved me some money.
Within minutes, we were in an examination room.
The vet came in and determined that Henry had a severe allergic reaction to the Benadryl. However, he was certain Henry would pull through as he was starting to regain some alertness.
Learn how to prepare for an emergency vet visit in this article.
I asked about pumping his stomach.
The vet informed me that within 30 minutes, the medication was already in his kidneys and any damage would’ve been done. So, it wouldn’t do any good. He said that pumping his stomach now would cause more discomfort for Henry.
The vet decided to give Henry some fluids and keep a watchful eye on him.
By that evening, about 12 hours later, Henry was back to his normal self, and I was able to fully breathe.
What Else Could I Have Done for Henry?
If I were thinking, I could’ve also called the pet poison hotline. They could’ve directed me on what to do or eased my mind. But honestly, it was most helpful to have a vet’s eyes on Henry and know that he’d be fine.
Could There be Another Cause for Henry’s Symptoms?
Of course. Nothing is absolute. However, when he was back to his regular self within the timeframe that the medication would take to cycle through his body, it was a good indication that it was the culprit.
But you never know there could be some underlying cause or combo of issues at play. Honestly, I’m really hoping that there isn’t.
How I Manage Henry’s Allergies Now
Since this incident with Henry, he’s been to see his regular vet for his semi-annual checkups.
His vet concurred that Henry has developed a severe allergic reaction to Benadryl. He did suggest I could use a different OTC allergy drug for him, like Claritin.
But honestly, I can’t deal with the possible side effects. If Henry’s allergy symptoms get extreme, then I’ll consider a different alternative. Perhaps a prescription allergy drug treatment.
For now, I’ve discovered some great natural remedies, which I list in this article.
Is the cost of your dog’s prescription meds too much? Here’s an article on how to safely save on your pup’s RX
Is it Possible for My Dog to Die From Severe Allergic Reactions or Side Effects of Benadryl?
Actually, yes! If your dog gets too much Benadryl or has a very severe allergic reaction, it could be fatal. That’s not a risk I’m willing to take.
How Much Did I Save With Benadryl for Henry
I know you’re curious about the breakdown of the Benadryl costs or savings for Henry over the years. Here are the nuts and bolts of it all:
| Cost of Benadryl (approx. 3 bottles over 5 years – $5.25 x 3) | $15.75 |
| Same-day Emergency vet visit | $147.00 |
| Gas to the vet clinic | $5 +/- |
| Emotional stress | Undescribable! |
| Possibly losing Henry | Unthinkable! |
It may be different for you and your dog. The point is to be aware that just because something is working today, it may not be tomorrow. So, always pay attention.
NOTE: I’ve now added Henry’s severe Benadryl allergy to all his tags, micro chip information, and highlighted with his vet records. Thanks to a kind reader for bringing this to my attention. If your dog is allergic to Benadryl or anything it’s a great idea to mark it for your pup as well in the same manner.
Related articles:
- Are There Really Safe Cheap Dog Meds?
- Emergency Dog Fund: How Much Money Should You Save?
- 15 Red Flags-Time For a New Vet!
- Easy Dog Emergency Vet Visits Tips
- Is A Dog Home Allergy Test Worth The Money?
- How to Find the Best Vet
- 14 Natural Remedies for Dog Allergies: Paw-sitive Relief!
- Hidden Dog Expenses: Why Good Dog Parents Spend More Than They Expect
FAQs About Benadryl for Dogs
Can dogs suddenly become allergic to Benadryl?
Yes. Unfortunately, past doses being fine doesn’t influence the next dosage. That’s what happened with Henry.
How long does Benadryl stay in a dog’s system?
It will depend on your dog, how active they are, and how much water they drink. But generally, Benadryl is out of most dogs’ systems within 12 hours or sooner.
What are signs of a Benadryl overdose?
There are a few signs, including:
- Lethargy
- Vomiting
- Unconscious
- Drooling
- Diahrrea
- Tremors or trembling
- Unable to walk
If your dog has any of these symptoms, contact your vet immediately.
Should I give Benadryl without calling my vet?
No. Always talk with your vet before giving your dog Benadryl, especially for the first time. Your vet knows your dog’s health and medical issues, and will be able to advise if this OTC drug is a good idea or not.
When should I take my dog to an emergency vet?
Call your vet or rush to the emergency vet if your dog is exhibiting any of these symptoms after taking Benadryl:
- Unconscious
- Diahrrea
- Drooling
- Wobbly while trying to walk
- Trouble or labored breathing
- Tremors or shaking
- Panting
Are there alternatives to Benadryl for dogs?
Yes, there are several, including fish oil and probiotics. You can see a complete list of alternatives for dog allergies here.
Can puppies take Benadryl?
Talk with your vet before giving a puppy Benadryl or any medication. The amounts are different, and most of the time it simply isn’t recommended for puppies.
Benadryl for Dogs: Key Takeaways
Most of the time, Benadryl will do exactly what it’s supposed to do and suppress your dog’s allergy symptoms. But it’s that one time when you mindlessly give your dog a dose that it could go sideways.
For me, I will never give another allergy medication to Henry. I will also make sure that whatever medications I give him, I do during office hours, if at all possible.
Why would a drug Henry’s taken for years suddenly have such a severe reaction? I asked both the emergency vet and his regular vet. Both had no idea, but both concluded it was the Benadryl and to avoid the drug at all costs. Of course, that was a no-brainer.
I still don’t believe Benadryl is automatically dangerous for every dog. Many dogs take it without problems. But Henry taught me something I’ll never forget, which is to never assume that because a medication worked yesterday, it will always be safe tomorrow. Paying attention after every dose only takes a few minutes, but it could make all the difference if something unexpected happens.
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Wow! That was scary! Thanks to your quick action and intuition in taking Henry to the emergency vet, his life was saved. It’s very unsettling to know that what had been working for years all of a sudden stopped working and had an alarming reaction. I’m glad Henry is okay and I don’t blame you for staying away from Benadryl going forward. I honestly had no idea pets could take Benadryl in the first place. I personally take Benadryl as needed during allergy season and also is the only antihistamine that works for my nut allergy (in case I need it). I wonder what other alternative natural medicines or tinctures exist to help dogs with allergies. Thanks for sharing your experience. This will be of great help to other pet parents.
That’s a good idea to look into natural alternatives to Benadryl. I’ll do that. Thank you for the support! It was definitely scary and one I never want to experience again.
Layla is allergic to Benadryl and I found out the hard way also but we caught it in time so I have stopped with all over the counter products for her but give her supplements which help immensely especially mushrooms.
I have it on all her tags plus that she is allergic to Benadryl to be safe also. I am happy Henry is ok and thank goodness you caught it in time
I had never thought of adding Benadryl to Henry’s tags. I’ll do that today and do an update to this article. Thank you for that bit of information. I’ll look into mushrooms too. Especially since they work so well for Layla. Thank you!
Wow the incident with Henry must have been terrifying. People need to know that these things can sometimes cause reactions. I would have been beside myself with an ill dog! Are there supplements or natural remedies you can get that ‘might’ work?
Yes, I was beside myself. But trying to put on a brave face for Henry and to attempt to do whatever was best for him. I think there are some natural supplements. I’m just starting to explore them. Thank you for your continued support!
OMG, Terri that allergic reaction with Henry must have been so scary! What an awful thing to have to go through. Your watchful eye and quick action probably saved his life. I can’t believe he developed such a severe allergy out of the blue like that. You have to be so careful with anything you give your pet, even when it is prescribed by the Vet. Thank goodness he is ok – that photo of him is just adorable!
You are absolutely correct. We must be very careful with everything we give our fur kids. I never saw this one coming since it worked so well for many years. That photo of Henry was just too much. He was not happy to be back at the week the next week and did not want to experience the thermometer up his bum again. He always gives me a huge hug when that happens. I’m sure it’s his way of saying “Why, mom, why?!” I can’t say I blame him. I wouldn’t enjoy it either. I really should’ve snapped a shot of him once we left the building. Happy little pup! Actually, I was too. He got a great check-up.
Holy Moly, what a fright! I am so glad that Henry was okay. But talk about scary. Now I never gave much thought about being allergic to the very medicine we give for someone having an allergic reaction! But why not, nothing is foolproof. I just never gave that one a thought. Double scary. I have used Benadryl, thankfully with no reactions other than the one we needed. One of my Huskies when she was just a pup, sat (yup, plopped her puppy behind right down) on an entrance to an in-the-ground bee hive. I came flying out of the house to my daughter’s screams as Harley was loaded with bees within seconds as she was blocking their egress and ingress from the hive! After tossing her a huge bath towel to wrap about her (so she wouldn’t get stung) and she ran with her to meet me, and we had to pick the bees out of her double coat and get her to the ER. Well. Her face was puffed right out and we were a wreck. The on-call vet gave her a shot and said she should be fine. When I got home and read the bill, it was for Benadryl. $125 for the ER and $150 for a shot of Benadryl! (This was a long time ago, I can only imagine how much it is now). After talking with my own vet, she recommended getting some to have on hand and gave me the proper doses, so I always had it in my Huskies’ first aid kit from that point on. Thankfully, Harley was fine and a decade later our Chloe was bit by something (I suspected a spider) and her poor nose and face swelled something awful. Thankfully I gave her Bendryl at home before we left for the vet and by the time we arrived, the swelling had thankfully reduced. I shudder to think what would have happened if they had been allergic to the antihistamine! Mind. Blown. I’m sharing this so it can help others be aware.
OMG!!! Poor Harley sat on a bee hive! Oh, how awful! I can’t even imagine. That would be an image I would never forget either.
You’re absolutely correct. I never once thought about Henry being allergic or never severely allergic or developing a severe allergic reaction over time to a drug that is designed for allergies. That almost seems crazy! Lessoned learned on that one though. I suppose it could happen with other drugs as well. Henry just developed it with Benadryl because he had taken it for 5 years. But now, I’m wondering if he’ll develop an allergy to his Heartguard, which he has taken monthly for 6 years. That’s a scary thought I hadn’t entertained that idea until now. I’ll move the time and day for that medication up so it’s during the vet hours M-F. Thanks for giving me that thought. And thank you for your continued support! I really appreciate it1
So glad to hear Henry is ok now what a dreadful scare for you, our old dog Badger used to be allergic to be allergic to spot on tick medications, when I got Boris I obviously didn’t want to risk using the spot on medication on him in case Badger came into contact with it, so I got Boris a tick collar Instead. We stood discovered Badger was allergic to that as well and had to rush him to the vets , thankfully he made a full recovery but it was touch and go for a while
It’s actually quite scary how many things can make our dogs unwell in a house x
Oh my, poor Badger! I’m glad you caught that he was allergic to the collar as well. That wouldn’t have occurred to me either, especially if it was on another dog (Boris).
You are absolutely correct, Dawn! There are so many things that can make our dogs and pets sick. We have to always pay attention because you just never know what may be an issue. Or if something that is working today will be a severe issue tomorrow.
Thank you for so bravely sharing your story of Badger and Boris. May your courageous story help others.