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All TopicsForum: Hormonal Therapy - Before, During and After → Topic: Tamoxifen and grapefruit/juice

Topic: Tamoxifen and grapefruit/juice

Forum: Hormonal Therapy - Before, During and After — Risks and benefits, side effects, and costs of anti-estrogen medications.

Posted on: Apr 16, 2012 01:07PM

claireinaz wrote:

Hi all,

Just sharing. I talked to my pharmacist this morning and he confirmed that grapefruit and or grapefruit juice interact with Tamoxifen, making it less effective. I used to eat it every day (as of yesterday) but won't anymore darn it.

It may have been on the package insert for tamoxifen but I probably didn't read it. I'm glad I checked in here and found that there seemed to be some concern about this issue.

He said other citrus fruit doesn't have the same enzyme so they are okay.  

He also said eating half a grapefuit a month probably would be alright.


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Apr 16, 2012 01:52PM geewhiz wrote:

Thank you for sharing that with us!!

Dx 10/2/2009, IDC, 2cm, Stage IIIA, Grade 2, 8/13 nodes, ER+/PR+, HER2+
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Apr 16, 2012 02:13PM jancie wrote:

If you go to www.drugs.com you can use their interaction checker to see all of the OTC and prescription drugs that interact with Tamoxifen.  You might want to do this as the list is HUGE!

Simple things like Benedryl, etc. interact with Tamoxifen.

Never Alone - My TaTa Sisters are always with me! Dx 12/30/2008, IDC, 4cm, Stage IIB, Grade 1, 0/5 nodes, ER+/PR+, HER2-
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Apr 16, 2012 11:05PM , edited Apr 16, 2012 11:18PM by peggy_j

My understanding is that grapefruit changes the rate at which your body absorbs tamoxifen and many, many other medications. (including common medications, like ones for high blood pressure.) Not sure why the pharmacist is saying that it's ok to eat a half a grapefruit once a month. If you really can't live without grapefruit, perhaps a better strategy would be to eat it after your know the tamox is fully absorbed. (2 hrs? 6 hrs???) I'd ask your doc. Personally I just skip it.

Edited to add: This source (below) says

"One standard glass of grapefruit juice is considered enough to cause significant impact to the metabolization of certain medications, especially if taken within four hours of each other, but the effect may last up to 24 hours. This interaction is particularly dangerous if the medication has a low therapeutic index, which means that small increases in dosage quickly become toxic. Grapefruit juice only affects the enzymes in the intestines and not those in the liver, so injected drugs are not a concern."


Dx 2/2011, IDC, <1cm, Stage IA, Grade 1, 0/3 nodes, ER+/PR+, HER2-
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Apr 17, 2012 09:03AM claireinaz wrote:

Peggy J, I asked him if I could take the tami at night and eat my grapefruit in the morning...he said no. So it's off my radar of foods for at least five years...

He said that it is an enzyme-metabolic reaction, as you've captured.

I knew about the benedryl already, and started checking further, b/c of the postings here. I don't know if I would have found it otherwise since my onc. never told me about interactions.  

It pays to be proactive about your health. No one is a better advocate for your health that you...


9/29/11 ILC, 2 c. stage II grade 1, ER/PR+ HER2-, 6/11 nodes, lumpectomy, DDAC x 4, Taxol x 12, 33 rads, Tamoxifen to arimidex, BMX/immed recon 7/3/13 "God supposedly gives us only what we can handle. God must think I'm a badass."
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Apr 17, 2012 11:14AM peggy_j wrote:

Good to know that the pharmacist thinks taking tamox at night isn't enough. I'm sticking to my no grapefruit plan.

FWIW, when I asked my MO about food interactions, she referred me to her nutritionist, who sent me a 20+ page printout from her database. For each substance that might have an issue, it gave the severity of the interaction and graded how solid the evidence was. Maybe you have access to a nutritionist who can share that same info? Some books list possible interactions. In one, I found that licorice root has a contraindication with tamox. So much for many of my favorite herbal teas! There have been other discussions here on various threads (often in the complementary forum), but it's nice to have one solid source.

Dx 2/2011, IDC, <1cm, Stage IA, Grade 1, 0/3 nodes, ER+/PR+, HER2-