Does Metamucil Interact With Benadryl Or Prednisone?
In our latest question and answer, our pharmacist discusses whether or not Metamucil interacts with Benadryl or prednisone.
I am taking Metamucil and am scheduled for a cat scan any day now. Can my doctors mix Metamucil with prednisone and Benadryl for my cat scan? I have had a bad reaction a few years ago so now the doctors always use prednisone and Benadryl for the scan. Google says I should not mix Metamucil with these other 2 drugs.
Aug 07, 2022- Metamucil can reduce how well Benadryl and prednisone are absorbed if taken at the same time because fiber forms a gel-like substance that interferes with drug absorption. Take Benadryl and prednisone at least 30-60 minutes before Metamucil or at least 2 hours after to avoid this interaction. If you're taking these medications for a CT scan, take your pre-medications as directed and take Metamucil later in the day instead.
Thanks so much for your question Maxine!
I'm sorry to hear you've had problems in the past getting a CT scan (also known as a 'CAT' scan). It's not uncommon to pre-medicate with certain drugs, like Benadryl and prednisone, to reduce the risk of a reaction to the contrast media used for the scan. This is especially true if you have had a reaction in the past.
Metamucil With Benadryl And Prednisone
In regard to taking both of these drugs (Benadryl and prednisone) with Metamucil (a psyllium fiber product), you should not take them at the same time.
This is a general rule of thumb for fiber products in general.
Metamucil, being a fiber, can significantly affect the absorption of drugs if taken at the same time. Generally, fiber decreases both the rate and extent of absorption of other drugs given with it since fiber forms a gel-like substance in the stomach when ingested. This may make these medications less effective.
You should, ideally, take any drugs at least 30-60 minutes before taking a fiber product like Metamucil or at least 2 hours after.
If you are scheduled for a CT scan on a certain day, I would just take your pre-medication regimen of Benadryl and prednisone as directed by your doctor and simply take your Metamucil dose later in the day to avoid an interaction.
Final Words
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References & sources
Glossary — Terms in This Answer
- CT scan
- A medical imaging test that uses X-rays to create detailed cross-sectional pictures of the inside of your body.
- Pre-medicate
- To give medication before a procedure to prevent or reduce unwanted reactions.
- Contrast media
- A special dye or substance injected into the body to make certain structures more visible on medical imaging scans.
- Benadryl
- An antihistamine medication used to reduce allergic reactions and itching.
- Prednisone
- A corticosteroid medication that reduces inflammation and suppresses the immune system.
- Metamucil
- A fiber supplement made from psyllium that helps promote digestive health and bowel regularity.
- Absorption
- The process by which a medication enters the bloodstream and is taken up by the body.
- Psyllium fiber
- A natural plant-based fiber that absorbs water and forms a gel-like substance in the digestive system.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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