Drug & supplement interaction

Agar + Sodium Phosphate (prescription drug)

Sodium Phosphate (prescription drug) brand name: Visicol.

Minor Interaction
Medically reviewed by · Updated September 2026
The bottom line Minor

Agar has a minor interaction with Sodium Phosphate (prescription drug). Agar forms a thick gel, which may disrupt the absorption of nutrients and medications.

Read the full interaction report
SeverityMinor
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Agar and Sodium Phosphate (prescription drug)

Here is the interaction we found between these two, with the evidence behind it.

Minor

ORAL DRUGS

Why this applies to Sodium Phosphate (prescription drug)

Sodium Phosphate (prescription drug) falls under ORAL DRUGS — the group Agar interacts with.

Agar forms a thick gel, which may disrupt the absorption of nutrients and medications. Animal research suggests that consuming a diet consisting of 5% to 10% agar alters the absorption of nutrients from the diet. In one study, consuming a diet composed of 10% agar reduced the absorption of all evaluated minerals. Theoretically, agar may also impair the absorption of oral drugs.
Severity Minor Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the thing to keep in mind: agar is a seaweed fiber that soaks up water and turns into a thick gel in your gut. In theory, that gel could grab onto things passing through and slow how well they're absorbed. Since your sodium phosphate prep works right there in the intestines to pull water in and trigger the cleansing diarrhea you need before a colonoscopy, mixing in a bulky fiber gel could blunt or muddy that effect.

Honestly, this is a theoretical concern based mostly on animal studies, not strong human data, so it's rated minor. Still, a clean prep matters for a good colonoscopy. I'd skip agar supplements around your prep days and follow your prep instructions exactly. Ask your pharmacist or doctor if you're unsure.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  2. Kondo H, Osada A. Influence of dietary fiber on the bioavailability of zinc in rats. Biomed Environ Sci. 1996 Sept;9(2-3):204-8.
  3. Harmuth-Hoene, A. E. and Schelenz, R. Effect of dietary fiber on mineral absorption in growing rats. J Nutr 1980;110(9):1774-1784. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Agar Also Interacts With Other Medications

Agar has 2,021 minor known drug interactions in our database — the Sodium Phosphate (prescription drug) one above is one of them. If you take anything else, check it against the full list below.

Minor 2,021 No known interaction 809 (incl. Sodium Phosphate (prescription drug))
Taking anything else?

Check Another of Your Medications Against Agar

Covers the 2,830 medications we’ve checked against Agar. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Sodium Phosphate (prescription drug)

This page covers Agar only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Sodium Phosphate (prescription drug) page lists 18 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Coffee Charcoal (moderate), European Mandrake (moderate), Glucomannan (moderate) and Guar Gum (moderate).

By severity: 1 major · 8 moderate · 9 minor.

From our pharmacist’s overview on the Sodium Phosphate (prescription drug) page

“Before you take prescription sodium phosphate (Visicol) tablets to clear your bowel ahead of a colonoscopy, this list deserves genuine attention, and the lone major entry, activated charcoal, is where I would start. Charcoal soaks up drugs in the gut, and nearly all 18 ingredients here, mostly fibers, gums, and mucilage-rich herbs like…”

Reviewed by 2 · Jul 18, 2026

Open the Sodium Phosphate (prescription drug) interaction page

One more smart check

Taking Agar as Part of a Dietary Supplement Product? Check It for Interactions

We hold 23 real supplement products containing Agar, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Agar. Your product may carry other ingredients that interact with Sodium Phosphate (prescription drug) too, on top of Agar — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Agar and Sodium Phosphate (prescription drug) Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Agar
Top half

#570 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Sodium Phosphate (prescription drug)
Steady interest

#1,586 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Agar

What is Agar?

Agar
  • Constipation
  • Weight loss
  • Vegetarian gelatin substitute
  • Source of dietary fiber
  • Appetite control

Agar is a plant-based gel made from red seaweed that is widely used as a vegetarian alternative to gelatin and as a source of dietary fiber. It is sometimes taken as a bulk-forming laxative or weight-loss aid, but solid human evidence for these health uses is limited. It is generally considered safe as a food, but you should drink plenty of water with it and check with your pharmacist before using it as a supplement.

Read the full Agar monograph & all interactions
Medication

About Sodium Phosphate

What Is Sodium Phosphate Used For?

Brand name: Visicol

Sodium Phosphate enema is used to relieve occasional constipation. It works directly in the rectum and lower bowel, and most people see results within 1 to 5 minutes of use.

It is a single-use, as-needed product — not something taken every day long-term. It is only for rectal use and should not be swallowed.

See full Sodium Phosphate drug information
Keep checking

Other Drugs & Agar

Browse every other medication we’ve checked against Agar — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
0Moderate
2,021Minor
808No known interaction
2,021 Minor 808 No interaction
Minor

2,021 interactions

Showing 60 of 2,021 minor interactions — see all 2,021 on the Agar page.

No interaction 808 drugs checked — show the list

We also checked Agar against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 808 medications checked with no known interaction — see the full Agar list.

See the full Agar interactions page
See every supplement checked against Sodium Phosphate (prescription drug), ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Agar monograph › Uses, safety, and every drug interaction in one place Sodium Phosphate (prescription drug) supplement interactions › Every supplement checked against Sodium Phosphate (prescription drug), ranked by severity Sodium Phosphate drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Agar and Sodium Phosphate (prescription drug) Together: Common Questions

Can you take Agar with Sodium Phosphate (prescription drug)?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Agar and Sodium Phosphate (prescription drug) interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Sodium Phosphate (prescription drug) and Agar?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.