Skip to content
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: September 29th, 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. 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?.”  […]

Scroll To Top