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

Bioflavonoid Quercetin has Anti-Cancer Effects

Updated: October 18th, 2018

Quercetin has been around for some time as it is a naturally occurring compound found in the peels of citrus, capers, certain herbs, onions, and grapes**. Quercetin is also found in the Chinese Scholar tree, one of the 50 fundamental herbs used in Traditional Chinese Medicine.

Quercetin has some interesting and fairly potent anti cancer effects. First, it has anti inflammatory effects.  We now know that cancer development and also cancer progression both rely on low grade inflammation in the body.  Inflammation that is low grade may not be visible to the naked eye.

Our bodies and those of our loved dogs are constantly barraged by a host of microscopic, damaging substances daily.  This creates inflammation.  Excess fat in the body creates inflammation.  A diet too rich in certain fats (omega 6 fatty acids) and lacking in others (omega 3 fatty acids) creates inflammation.  Smoke, pesticides and herbicides, inhaled exhaust can all create this type of inflammation.  Finally, cancers themselves created inflammation.

Quercetin is able to partially block the very same enzymes that are targeted when vets and oncologists use anti inflammatory medication as a part of metronomic chemotherapy. This kind of chemo is low dose, and may help to help lessen the blood flow that helps feed developing or spreading cancers.

This compound also has been shown to attack human breast cancer cells (in a test tube) in a way that is similar to some of the new dog cancer drugs, Palladia and Kinavet K-1 (masitinib).

An injected form was found to shrink sold tumors in mice.  But what about taking it as a pill?  This works too, but we need to protect it from being broken down so it gets in the bloodstream (this is the method used in Apocaps, and it was for these reasons that rutin, a rich source of quercetin, was included in the Apocaps formulation.).

So how can we use this interesting substance?

First, we need to be sure that we are not creating anti oxidants which could interfere with some chemo drugs and other helpful strategies (these are outlined in the Guide).  If we use larger doses of quercetin, we can overcome this effect.

Secondly, we should think of quercetin for tumors of the stomach or intestine which will get the highest dose of a tablet taken by mouth.  Quercetin does have other uses, but this is one easy one to remember.

And it has been shown to be safe. 🙂

All my best

Dr D

**Note that onions and grapes may create toxic reactions in dogs.

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Leave a Comment

  1. Joan Trojan on July 27, 2012 at 3:03 pm

    Dear Dr. Dressler,
    I just bought your guide, and I am getting ready to buy Apocaps and K9
    Immunity for my beautiful greyhound, Lily, with osteo.She had amp on 12/16/11-5 rounds of carbo-no mets yet. I am also giving artemisinin(sp?) and n acytyl
    cysteine (600mg a day-the vet wants to try it-he said he had good results with
    one dog), and a probiotic. Could you please guide me with the correct way to
    space these out throughout the day? Also, I’m worried about the NAC and
    whether it’s OK to give-would like your input. Also if you feel the NAC is OK-how would I dose it with everything else I am giving? Thank you so much for all you do to help us fight this cancer.

    Thank you,

    • Dr. Demian Dressler on August 1, 2012 at 1:50 pm

      Dear Joan,
      sorry to hear about Lily. OSA is common in the breed.
      There is a section in the Guide called the supplement hierarchy which discusses NAC.
      The use of this supplement in this case with these other supplements on board is a confused choice. The mechanisms of NAC and the other meds hinder each other.
      I hope this helps.
      Dr D

  2. Joan Trojan on June 19, 2012 at 1:53 pm

    Dear Dr. Dressler,
    I just bought your guide, and I am getting ready to buy Apocaps and K9
    Immunity for my beautiful greyhound, Lily, with osteo.She had amp on 12/16/11-5 rounds of carbo-no mets yet. I am also giving artemisinin(sp?) and n acytyl
    cysteine (600mg a day-the vet wants to try it-he said he had good results with
    one dog), and a probiotic. Could you please guide me with the correct way to
    space these out throughout the day? Also, I’m worried about the NAC and
    whether it’s OK to give-would like your input. Also if you feel the NAC is OK-how would I dose it with everything else I am giving? Thank you so much for all you do to help us fight this cancer.

    Thank you,

  3. Krystyna K on June 19, 2012 at 10:48 am

    Dear Dr. Dressler,
    My 8 1/2 year old lab mix, Lucky, the light of my life, has been diagnosed with regenerative anemia. Today, after doing an abdominal ultrasound, multiple cavitated tumors were found in his spleen. The fluid is likely blood and explains his anemia and lethargy. Approximately 75% of spleen masses in dogs are hemangiosarcoma which, as you know, is an aggressive tumor of blood vessels that has a high rate of spread. Tomorrow, his spleen is being removed and a biopsy will be run. Treatment consists of removal of the spleen and followup chemotherapy which will be a combination of an injection in the vein and an oral tablet every 3 weeks for a total of 6 treatments. If it turns out to be hemangiosarcoma, his prognosis is not good. Average survival is 6-8 months. My question to you is will the apocaps help in our situation?
    Thank you so much for your consideration. I look forward to hearing from you soon.
    Sincerely, Krystyna K

  4. Bill on June 11, 2012 at 4:32 pm

    Hi Dr. Dressler,

    Thank you for taking time to address fellow guardians’ questions to extremely complex and emotional issues that must be difficult to answer in a blog format. I have been extremely fortunate to have had my dog, Charlie, a pekingnese, for the past twenty years. My bond with him has grown over these years more than I could have ever imagined, as with most guardians, which does not prevent the inevitable from being exceptionally difficult. He has been through many health issues over the years successfully but now has come to an obstacle which I have been told is insurmountable I assume because of his age and its nature. He was diagnosed with a brain tumor two days ago. He redeveloped seizures about 6 months ago, after a three year hiatus, and started circling four days ago. I just purchased your book and Apocaps awaiting their arrival. Charlie was prescribed Prednisone, Phenobarbitol with a low dose of Sodium Bromide (seizures), and just today, Soloxine (thyroid supplement) due to his blood test. I read Phenobarbitol could inhibit the metabolism of protein. Will any of the meds that Charlie is on affect the benefits of Apocaps and the diet recommended in your book?

    Sorry for a long question that I thought would be two sentences. My emotions are extremely high and need the exercises in your book to strengthen the guardian so that we can take the best care of our loved ones.

    • Dr. Demian Dressler on June 14, 2012 at 12:25 pm

      Dear Bill,
      I am very sorry to hear about this. 20 years is quite a long time.

      These apply:
      My dog is on seizure control medication. Can I use Apocaps?

      There have been no reported adverse consequences or interactions of Apocaps use in dogs on seizure control medications. However, in human literature, there are reports of glutamine decreasing the effectiveness of seizure control medication in people. A small amount of L-Glutamine is used in Apocaps. Like all health care steps, consult with your veterinarian before using Apocaps. If this is not possible, we advise avoiding the use of Apocaps use in dogs on seizure control medication as the very safest recommendation.

      Can I give Apocaps with prednisone, prednisolone or other anti-inflammatory agents?

      Yes, but with some caution. Some of the ingredients in Apocaps have an anti-inflammatory effect, so we recommend thinking of Apocaps as a mild anti-inflammatory and following the guidelines generally offered with prednisone and NSAIDs (non-steroidal anti-inflammatory drugs).

      We recommend reducing the dose of Apocaps to a half or quarter dose if you are using prednisone or any NSAIDs. Or, if preferred by your veterinarian, you could reduce the dose of the anti-inflammatory, prednisone, prednisolone or NSAID to half or quarter dose. The choice of which to lower would depend upon the effect desired.

      Okay, more reading for you:

      I hope this helps
      Dr D

  5. Lynn on June 5, 2012 at 7:29 pm

    Hi Dr. Dressler
    I understand that your interest is in dogs but I have a 16 year old cat with Oral Squamous Cell Carcinoma. He has undergone chemotherapy and stereotactic radiation. At this point all I can do is wait to see if the tumor will begin to grow. We have no Holistic veterinaries in our area. I was wondering if you are aware of tumor suppressing herbs or supplements that I would be able to use to give him a chance to live longer. I have read about the benefits of Quercetin , certain mushrooms and herbs etc and if any of them have good success rates and if so which ones. I am basically on my own trying to find something since I live so far away from anyone offering consultations. At this point I feel helpless and desperate to find our what to do next with my cat’s life hanging in the balance. I heard that yo were the best.

    • Dr. Demian Dressler on June 14, 2012 at 12:50 pm

      Hi Lynn
      I think we addressed your question via e-mail.
      This blog is for dogs as you know (although my “interest” includes cats too!)
      CAS options for kitties
      I’m a little leary of quercetin in kitties as the mechanism is a bit dicey.
      I’d be feeding the cat jd too and metacam.
      Everything should be done under veterinary supervision too…
      I hope this helps
      DR D

  6. mike m on May 15, 2012 at 5:09 am

    dear dr dressler

    my 11yo golden retreiver has an anal gland carcinoma that is reoccurring. he had surgery last july which was very successful but now the tumor is 7x3cm and causing defacating problems. since last july we bought your book and started fish oil,garlic and apocaps. my dog weighs 105lbs and is on enalapril for hbp
    what daily dose of apocaps is appropriate and does k9 immunity help retard growth for this kind of tumor? the surgeon advised us against surgery again due to a poor prognosis because tumor is strongly attached to the rectum walls.
    any options available cryo or injectables?
    i love your book thank you for all the helpful advice

    • Dr. Demian Dressler on May 18, 2012 at 9:37 am

      Dear Mike,
      Sorry about your Golden.
      I am wondering, have you read the seciton on supplement heirarchy and excluded supplements? Since you have the book, you can find the discussion of garlic as a lower priority supplement. There is no different dose for Apocaps. I would also be discussing with your vet the use of Neoplasene and intralesional Matrix 3 cisplatin impregnated beads. K-9 immunity does not directly retard the growth of the tumor but likely helps the immune system, which is often suppressed when coping with cancer.
      I hope this helps
      Dr D

  7. Chris on May 9, 2012 at 5:27 pm

    Thanks Dr. Dressler.

    I am in complete agreement with your thoughts on changing if something’s not working being common sense.

    • Dr. Demian Dressler on May 18, 2012 at 9:54 am


  8. Richard Breese on May 3, 2012 at 6:30 am

    Dr. Dressler,

    Hello, i read a post on april 20 from Valerie Gentile Sachs stating that her German Shepard-Mayahad passed and i am sorry to hear that i am going through a similar ordeal with osteosarcoma in a 8.5 year old male Akita named Bear. I was wondering if the full and half bottle of Apocaps she has offered is still available so that i may use them on Bear my e-mail is rjbreese@discoverknoxville.com, this would be greatly appreciated, thanks. Richard Breese and Bear.

    • Dr. Demian Dressler on May 9, 2012 at 4:09 pm

      Dear Richard,
      I am sorry to hear about your Akita. I would contact Ms. Sachs directly as she is an independent Guardian.
      Dr D

  9. tracy knuth on April 29, 2012 at 2:32 pm

    Dr Dressler, another question for you. What would your opinion be on trying Doxycyline for Mast Cell Tumors? Sasha has no bone involvement that we are aware of, but I see in your book in can limit tumor growth,
    Thank you again,
    Tracy Knuth

    • Dr. Demian Dressler on May 9, 2012 at 4:21 pm

      Dear Tracy
      It is a medium priority supplement. Check the supplement hierarchy in the Guide. If you are already using the higher priority supplementts I would consider it under veterinary supervision.
      All my best
      Dr D

  10. Chris on April 28, 2012 at 6:10 am

    Hi Dr. Dressler. I spoke with our oncologist as you suggested and she said that she thought that 72 hours after stopping the piroxicam would be enough time as well. She also said that before she could say what her thoughts were on that approach, she’d want to be able to see two things:

    1. MIC (not sure what this means, she just called it out as something in which she’d be interested)
    2. Any data around concentration of the medication in urinary excretion

    She explained with respect to the second one that because it’s bladder cancer, if the apocaps is effective in reaching the bloodstream, but dilutes before it gets to the urinary tract, it would probably not be particularly efficacious in attacking the TCC since it’s the urine that delivers any chemotherapuetics to the bladder.

    Is there any data I could provide her around these two numbers?


    • Dr. Demian Dressler on May 9, 2012 at 4:25 pm

      Dear Chris,
      nope, I don’t have any data on urinary excretion. Just teaming up now with Dr. Phil Bergman who developed the melanoma vaccine to do a multicenter clinical study, so that data will likely be available in the future. However, I can say that if something is not working, it seems basic wisdom to try something else.

  11. Chris on April 25, 2012 at 3:30 pm

    Dr. Dressler, with respect to Apocaps, sometime back it was noted that it is necessary to work with your oncologist before using them if your pup is on an NSAID, because apocaps do exhibit some degree of NSAID side effects. My girl Osa has TCC of the bladder and has been on piroxicam for the past 10 months, and for that reason I have not used apocaps. I don’t feel that the piroxicam is helping, and am considering taking that out of her regimen and starting with the apocaps.

    But her BUN count is pretty high, around 49. If I do take her off of piroxicam, should I wait a while before starting the apocaps, or are the NSAID-like side effects of apocaps “low grade” enough that I could start them right away after stopping piroxicam?


    • Dr. Demian Dressler on April 25, 2012 at 6:37 pm

      Dear Chris
      if the urine is also dilute, we have kidney disease of some kind, possibly (but not necessarily) related to the TCC. See if the urine is dilute also so we know this is not just dehydration.
      I don’t worry much about wash out with piroxicam. I would only wait about 2-3 days personally but do check with your vet. Also you might consider oral Neoplasene which I have been using along with Apocaps for some dogs and in the low number so far we are doing okay. But again make sure your vet is involved with this.
      I hope this helps
      Dr D

  12. Judith Kiplinger on April 24, 2012 at 2:48 am

    Dear Valerie,

    I was sorry to read about Maya’s passing but encouraged that you were able to help her stay well for more years! If you still have the extra apocaps, we could sure use them!

    Blessings, Judith

  13. Judith Kiplinger on April 23, 2012 at 3:05 pm

    Dear Dr. Dressler,

    My almost 3 year old Tibetan Terrier appears to have lymphoma. We had a fine needle aspirate done today. Lymph nodes have been swollen for three months but they had him on doxcycline thinking that it may have been a tick-borne illness. The lymph nodes continued to grow and now they believe it could be lymphoma. His breathing is shallow and he drinks more water – otherwise he doesn’t exhibit any other signs of illness. The choices they have given us include weekly chemo for 6 months, chemo every three weeks for six months, and prednisone alone. We also have started him on the Johanna Budwig protocol – flax oil and cottage cheese blended together, raw foods. We are holistically oriented and believed initially that we wouldn’t do chemo, but the vet said he could still have good quality of life (if he tolerates it) and so now we are considering it more seriously. We are of course devastated. He is the heart of our home and our baby boy! Do you have any suggestions? We are ordering your book. Should we also try apocaps? Many many thanks, Judith
    P.S. All of this surfaced after his rabies booster shot.

  14. Juanita on April 22, 2012 at 10:02 pm

    Dr. Dressler
    Juanita Again. Sorry Emma & Tami is not sick. Would just like a good daily supplement. Our vet’s here don’t recomend anything spesific. Just want us to do the yearly boosters. Which you reccomend 3 yearly.
    Thank You

    • Dr. Demian Dressler on April 25, 2012 at 6:54 pm

      Dear Juanita
      I would suggest every 3 year vaccine boosters after year one for parvo and distemper. This of course does not mean every 3 years you go to the vet! Still do the annual or semi annual visits to be sure your loved ones are healthy. The top daily supplement will be Everpup which will be available in about 6 weeks.
      Dr D

  15. Juanita on April 22, 2012 at 9:58 pm

    Good Day Doctor Dressler
    Al the way from South Africa Cape Town,
    Would just like to ask, I have two Jack Russell Doggies Emma 7 & Tami 4. Could I give them apotaps for a daily supplement??
    Thank You So Much for doing such good work.

  16. Elaine on April 22, 2012 at 6:36 pm

    Could you please elaborate on what is considered a “larger dose” if I were to give it orally?

    Thank you!
    Elaine & Sunshade (18 months cancer survivor on Apocaps rotation with Artemisinin)

    • Dr. Demian Dressler on April 25, 2012 at 6:55 pm

      Dear Elaine,
      no need for it while on Apocaps. The rutin takes care of the quercetin needs as rutin produces quercetin in the body… 🙂
      Dr D

  17. tracy knuth on April 21, 2012 at 3:27 pm

    Dear Dr Dressler
    My 8 yr old golden retriever has had a mast cell tumor removed and has a second one growing quite quickly from the size of a golf ball to a grapefruit in a matter of 4 weeks. she has been taking prednisone since her surgery. I would love to try Apocaps, but since pred. is an anti inflammatory, and my vet was not familiar with Apocaps, she was unsure how to proceed. Any suggestions are appreciated.

    • Dr. Demian Dressler on April 25, 2012 at 6:59 pm

      Hi Tracy,
      under these circumstances I usually drop the pred (or the Apocaps) to half dose and give with a full meal and monitor for digestive upset.
      I hope this helps
      Dr D

  18. Valerie Gentile Sachs on April 20, 2012 at 9:30 am

    Dear Dr. Dressler:

    2 years ago our dog, Maya, was diagnosed with renal carcinoma. Her prognosis was poor – I was told she had about 6 months to live. I bought your first book and worked with it to develop an immediate and longer term response. We were included in your 2nd edition. She passed away last week. She was a 90+ lbs. German Shepherd and I do believe our response to her cancer gave her the opportunity to live a long, productive life. She was 11 1/2 when she died. Thank you for helping me.

    Now, perhaps I can help a bit in return. I have one full and one partial bottle of Apocaps. I would be happy to send them on to someone who can use them.


    • Dr. Demian Dressler on April 20, 2012 at 6:16 pm

      Thanks Valerie, I am very pleased you were able to extend her life with good quality and quadrupled estimated life span. Great work. As to your supplies, I might touch base with the other folks posting comments to send some. Look for the new posts and read the comments and I am sure someone will take you up on the offer.
      All my best
      Dr D

  19. J. Dade on April 20, 2012 at 7:39 am

    I have read that grape skins and quercetin which is the active agent in grape skin tht fights cancer is dangerous and in fact, toxic to dogs. Can you please respond to this. Thank you

    • Dr. Demian Dressler on April 20, 2012 at 5:58 pm

      Dear J. Dade,
      A good question. the toxic agent in grapes is not yet known. The safety publication is linked in the bottom of the blog for your reference. Please cite your source and i would be happy to review the documentation and comment on it-
      All my best
      Dr D

  20. Judith on April 20, 2012 at 3:42 am

    Dear Dr. Dressler,
    I found this article very infiormative. I have your book and I have been using Apocaps on my older dog with some success – but it stopped working.
    Bonnie has a solid external tumor on the back of her thigh. It was diagnosed as malignant a year ago. We tried cryo-surgery (was done by Dr. Goldstein, Smith Ridge Veterinary Clinic), It was only partially successful as the tumor never died off completely. We had another cryo-surgery last November, which did even less. So I started Apocaps and the tumor started shirnking. When I stopped Apocaps, it started growing again. So now I make sure I always have a supply of Apocaps, but it suddenly stopped working and the tumor is growing again.
    So my question is, would it be possible for my vet to obtain liposomal Quercetin and inject it into the tumor? Have you ever tried this? Any advice you could give would be appreciated.
    Thank you!
    P.S. I have just started adding K9-Immunity and K-9 Transfactor to her regimen. She was on CAS-Option before.

    • Dr. Demian Dressler on April 20, 2012 at 6:14 pm

      Hi Judith
      sounds like you have a mutating tumor (almost always the case at some point…).
      Hard to get what you are looking for. I might be looking at injectable neoplasene for this effect or perhaps insert matrix 3 cisplatin impregnated beads in the tumor for local chemo.
      I hope this helps
      Dr D

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