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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Do Tagamet and Benadryl Cure Cancer?

Updated: November 12th, 2021


Do Tagamet and Benadryl cure cancer in dogs? Sadly, it’s not that simple. Learn the role these drugs can play as PART of your dog’s cancer treatment plan.

There is a lot of buzz in online forums saying that the drugs Tagamet and Benadryl cure cancer in dogs. Some people say the Tagamet/Benadryl cancer remission protocol for dogs has a 99% cure rate for any cancer.

It sounds like a dream come true: cheap, over-the-counter medications, relatively safe to give to your dogs, and curing any type of cancer.

Except for one annoying little detail: Does it actually work?

We decided to look into this because some of our readers have tried the Tagamet and Benadryl protocol, and it didn’t help their dogs. Okay, not everything works for every dog or every cancer. We all know that.

But when they posted about their beloved pets not responding to treatment on forums dedicated to the Tagamet/Benadryl cancer remission protocol for dogs, instead of getting sympathy… their comments were deleted.

Which begs the question: is that 99% cure rate accurate? How do we know the real stats if failures are deleted and erased?

Without knowing how many failures there are, how do we really know how much of a risk this is?

We asked Dr. Nancy Reese, DVM, PhD, to look at the evidence for us for an episode of Dog Cancer Answers. (The full podcast is below.)

Benadryl and Tagamet for Mast Cell Tumors

First, a little background. Prescribing the over-the-counter drugs Benadryl and Tagamet is common practice for dogs with mast cell tumors. That’s because they can help with symptom relief and surgery in that particular cancer.

Mast cells are a normal part of your dog’s immune system. They contain granules full of histamine. When part of the body is damaged by an injury, bacteria, or viruses, the mast cells release their histamine.

The histamine causes swelling and inflammation, and can even cause hives and an uptick in stomach acid production. While these symptoms sound unpleasant, they help to attract more white blood cells to fix up the damaged area and boot out any invaders. This is good!

But when a mast cell becomes cancerous, it gets out of control.

And an out-of-control mast cell can pump out a lot of histamine… which can make your dog really, really uncomfortable. Digestive upset, itchiness … really uncomfortable.

As Dr. Nancy points out, histamines may fuel cancer cell growth in certain cancers. How exactly is not totally understood, but the presence of histamine MIGHT help cancers along. Prescribing antihistamines is routine in certain cancers in humans for this reason. But does that mean an antihistamine can stop cancers from growing, or better yet, reduce them?

Not exactly, not completely, and certainly not to the extent promised in these online forums.

Tagamet and Benadryl for Dogs

Diphenhydramine (brand name Benadryl) and cimetidine (brand name Tagamet) are both antihistamines that work to block histamine receptors on cells.

For a dog with a mast cell tumor, giving an antihistamine can provide some much-needed relief.

Mast cell tumors pump out histamines that cause inflammation. Giving an antihistamine provides relief.

Giving Tagamet and/or Benadryl can make a mast cell tumor appear to shrink, because the tumor is no longer swollen with histamines. This makes your dog feel a lot better! But is it really reducing the tumor itself? No.

It does, however, makes surgery to remove the tumor a lot easier, because your vet has a smaller region of inflamed tissue to remove.

So Tagamet and Benadryl can help dogs with mast cell tumors in two ways: symptom relief and easier, less messy surgeries.

Dr. Nancy says that Tagamet also has some mild anti-cancer effects that can be beneficial for melanoma in dogs.

Despite these benefits, Tagamet and Benadryl are not a miracle cure for cancer.

Dr. Nancy says, “If there was something that was easy, like Tagamet and Benadryl, that would cure cancer, I would buy stock in Benadryl and Tagamet!”

Dr. Nancy cautions owners about believing therapies that sound too good to be true.

And definitely don’t delay treatments that are scientifically and clinically proven to help fight and even reduce cancer in order to chase after a fad protocol.

Look for Facts, Not Stories

When evaluating a potential treatment for your dog with cancer, look for good science.

Good science is a treatment that has been used the same way in the same situation multiple times and given consistent results.

Good science also reports the failures, as well as the successes. And good science definitely does not tell you to refuse other treatments that may help your dog more.

Make Sure You Have a Good Diagnosis

To know if a medication truly fights or cures a disease, first you need to have an accurate diagnosis.

Tagamet and Benadryl are great for relieving itchy rashes from insect bites, which can often look similar to an irritated mast cell tumor. If the dog’s owner doesn’t get a diagnosis from their vet (requiring at least a fine needle aspirate, ideally a biopsy), you don’t actually know if the red lesion that resolved was a mast cell tumor or not.

Bug bites can look like mast cell tumors. Without a diagnosis, do you really know the healed lesion was a mast cell tumor?

Consider Whether Other Treatments May Have Helped

Other treatments and medications that the dog is on have to be considered too.

For example, if the owner started five different supplements and medications at the same time, sure, it might have been the Tagamet and Benadryl that did the trick.

But it also could have been one of the other things. You just don’t know.

Some of the folks who promote this “protocol” suggest that using only Tagamet and Benadryl is the best way to treat your dog. They say that other medications and supplements — and even dietary changes — will “neutralize” the protocol and cause it to fail.

This means that some people are forgoing solid treatment options in favor of this one.

That would be fine if it were reliably curing cancer. There is no doubt that some dog owners firmly believe that they have cured their dog’s cancer because they gave these two drugs in the doses and schedules recommended.

But without having formal studies and/or actual clinical use in place, it’s just impossible to know for sure if they are actually right … and if this is worth trying with YOUR dog.

After all, cancer is an urgent situation. You want to use a treatment that is reliable, where you know the chances of success ahead of time. Everything else is much more of a gamble.

Let’s look at how we determine whether a treatment is useful.

Formal Studies and Historical Use

Formal research studies look at a bunch of dogs with the same diagnosis and give consistent doses of the medications being evaluated. Then the dogs are all monitored in the same way to measure response to treatment.

A good study should also be easy for someone else to repeat, and the repeat study should get the same results.

If they don’t, then one of the studies probably had some other factor involved in the results.

If there aren’t formal studies available, but a method has been used for a long time with routine success, that’s also a good sign. This is called “historical use.”

Many treatments do start out as anecdotal tales of success. But urban legends that pop out of nowhere and have limited data are not a substitute for good science.

When evaluating a treatment option for your dog, you and your vet need to be able to see both the good and the bad about it. No treatment is perfect. But you need access to accurate information that tells the whole story.

Bottom Line for Tagamet and Benadryl

Tagamet and Benadryl are almost always beneficial for dogs with mast cell tumors and are usually prescribed for that reason. Mast cell tumors can cause digestive upset, hives, and terrible itching. These two histamine blockers really help reduce those symptoms. They are great for life quality!

They also reduce swelling, making mast cell tumors easier to remove with surgery.

If your dog has melanoma, they may also help. But for all other cancers, we don’t have solid evidence that they are a miracle cancer-fighting team.

We don’t have good studies. We don’t have a long history of use by many veterinarians (like we do for many other treatments and supplements). We have some people telling their stories on the internet and a suspicious pattern of deleting stories that don’t support the protocol.

Absolutely ask your vet about adding one or both to your dog’s cancer treatment plan, but don’t bet the farm on them. Focus on treatments that are proven to help fight and reduce your dog’s type of cancer.

You can read the full transcript of the interview on the episode page on the Dog Cancer Answers website.

Here is the video version of the podcast:

Please subscribe to, rate, and review Dog Cancer Answers in Apple Podcast or on your favorite pod-catcher. It really does help the show!

Paws and wags,


PS: Feel free to share this article or the podcast itself with your veterinarian and their staff.

Have a Great Question for Dog Cancer Answers Veterinarians?

Call the Listener Line at 808-868-3200

Leave a Comment

  1. Daniel Valverde on October 27, 2023 at 9:38 am

    I am a human being who has been taking Tagamet as an anti-cancer drug since 2010. I first heard about Tagament and cancer from my father in law, who was involved in AIDS research back in the ’80’s. (He is somewhat famous for having developed an off-label treatment for AIDS and autoimmune disorders called Low Dose Naltrexone). He had heard through colleges at the time that Tagament had potential as an off-label adjunct treatment for some cancers. My understanding is that small scale studies were done that were extremely encouraging; however, there will never be large scale studies done by the pharmaceutical industry because Cimetidine is out of patent, and without those large scale studies, Tagmet will never be embraced by the medical community. Years later, when I was diagnosed with stage 3 melanoma, I was told that my best option was a lymph node dissection, and that the success rate for that surgery was about 30%. Remembering what I had learned years earlier, I found a physician who agreed to prescribe Cimetidine at the anti-cancer dose. I had the surgery and have also taken Tagamet every day since, and have been cancer free ever since. Some years after that, my 17 year old cat was diagnosed with a cancer, either lymphoma or stomach cancer (we never did the biopsy). He was having stomach pain, so we decided to put him on Cimetidine and Low Dose Naltrexone. The Cimetidine was given both as an anti-cancer treatment and to ease his stomach discomfort. He went into full remission; the tumor vanished. Some time later he was examined by a different vet who, when told that he was likely cured by the Cimetidine said, “it that was true, everyone would know about.” It is exactly because of the skepticism of well-meaning health care professionals that everyone doesn’t know about it, or does not take it seriously.

  2. Becky on November 28, 2022 at 12:20 pm

    My 18 month old Basenji was diagnosed with Ostersarcoma after amputation of her Right foreleg. Oncologist discussed Chemo, but survival past 6 months was not projected.
    We started Palative care and Prayer. We give Benadryl, Vit C, Onco Support & Omega 3. That was May 2017, She is still with us & Cancer free.
    I also had a Basenji develope Mast Cell on the inside of her hind legs. Diagnosed with surgical biospy. Started her on Vit C & Benadryl 3 times a day. Six months later she was free of the Mast Cell. She is 14 now & still free of Mast Cell.

  3. Charbel on November 9, 2022 at 7:30 am

    Hello, fantastic and very interested article, i learnd a lot from it. It is written with simple Language that everyone can understand. Thank you!.
    I have a question: my dog had been diagnosed with mast cell. One day I gave her one tablet of ofloxacin (which the vet prescribed me) and after half hour my dog became very uncomfortable, panting and breath fast and was making voice that give me feeling she is feeling very bad. Now I read this article and mybe think that my dog reaction was from the histamine release. Day after the vet find she has spleen tumor.
    If there is here a veterinarian who can give me answer I will be very thankful.
    Is my dog reaction was from the ofloxacin or from the histamine from her cancer?
    Thank you very much.

    • Molly Jacobson on November 16, 2022 at 3:36 pm

      Hi Charbel,

      It’s hard to say why panting and fast breathing was happening at any specific moment. It might have been the antibiotic, since it was so close — maybe it hurt her stomach? But if you gave her more doses as recommended, and didn’t see it, that might not be it. Yes, it could be histamine release, but usually a dog in histamine overload has it for a while, because it takes a while to break down that histamine. (That’s why we give anti-histamines, to help break down those histamines.)

      Panting and breathing fast could also be a sign of anxiety, for example. Those symptoms don’t point to just one cause. Unless it has continued and really bothers her, I would set aside your question as one of those “unanswerable” ones.

  4. Lacey on October 8, 2022 at 3:38 am

    I thought the article was very informative and helpful. Thanks for explaining the mechanism behind antihistimines and acid reduces in their effects on MCT cancer.

  5. Kari Mogensen on March 24, 2022 at 5:37 am

    Bless your heart! Sounds like you’ve got an issue with pet owners trying OTC drugs on their dogs with cancer. And this statement takes the cake. We don’t have good studies. We don’t have a long history of use by many veterinarians (like we do for many other treatments and supplements).

    Funny how the internet brings all kinds of people together, from all walks of life with all different issues with their pets and we can decide from their stories which course of action we want to take with our dogs and OTC drugs. A vet tech for 5 years and all of a sudden you are an expert on dog cancer! SMH. The veterinarian profession is contributing to the rise in cancer of pets, with preventative poisons and vaccines. Keep that revolving door going huh? How much did you get paid to write this article? Let’s see if you delete my comment.

    • Kate Basedow, LVT on March 24, 2022 at 8:46 am

      Hi Kari! Please reread the bottom section with the heading “Bottom Line for Tagamet and Benadryl.” These drugs actually ARE beneficial for mast cell tumors, and may be helpful for melanoma as well. My recommendation (which was formed based on information from a veterinarian of 30+ years as well as independent research) is to consult with your dog’s vet or oncologist before starting them. Personally, I have given OTC drugs to my dogs for a couple different conditions over the years. Each time I got a diagnosis first so that I knew what the actual issue was (one of the frustrating things about medicine, as I’m sure you have experienced, is that multiple problems that are actually very different can look the same when taken at face value), and then made sure I had a safe dose for my dog’s current weight. OTC drugs can be very useful. BUT, giving OTC drugs willy-nilly can also be extremely harmful.

      • Corinne on June 9, 2022 at 8:33 pm

        I agree, this article was incredibly negative with very little other suggestions. If someone decides to try this method for their pet, which they acquired, it is entirely ip to them. Just like herbal supplements. Vets offer expensive options that many can not afford and will in the end suggest we euthanize at a last cost. Vet Tech is not a veterinarian. The internet loves letting anyone post their opinion. Search a little further and you will find actual studies, by Doctors on this. If I can treat myself OTC, I can treat my pet as well.

        • Mich on June 2, 2023 at 4:39 pm

          Of course the other suggestions are nonexistent because she wants you to search her blog and use her treatments. Ha

          • Kate Basedow, LVT on June 3, 2023 at 1:30 pm

            Hi Mich – what I want people to do is take a dog with cancer to a veterinarian (better yet, an oncologist if that is an accessible option). This is the only way to get an accurate diagnosis, which then informs the treatment options that you have.

  6. AmyLytle on October 27, 2021 at 4:34 pm


  7. Cimetidine anti-cancer effects for mast cell tumors on September 23, 2021 at 6:27 am

    […] Science is always changing, so if you are considering using Tagamet to “cure” mast cell cancer, please check out this important discussion with Dr. Nancy Reese, DVM, PhD, on The Dog Cancer Answers podcast, “Do Tagamet and Benadryl Cure Cancer?.”  […]

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