Herb & supplement monograph

Agar Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Agar interacts with medications. The heart of this page is the interaction list — every drug Agar is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Agar is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Interaction report

Drugs that interact with Agar

2022 medications have a known interaction with Agar, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Agar using our pharmacist-reviewed interaction data.

AI summaries are generated from our Agar interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction 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.
Possible. 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
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Agar combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Agar affects

Every type of medication (drug category) Agar is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 1 drug category Agar interacts with

Oral Drugs

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.

Likelihood Possible Evidence D

Monograph

Agar: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

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.

Part used: Cell wall extract of red algae (seaweed)
Common forms: Powder, flakes, bars, capsules, food-grade gel

People commonly use it for

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

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

Generally safe as a food, but supplement doses should be taken with plenty of water to avoid blockage.

PregnancyInsufficient reliable information

Insufficient reliable information available; avoid using.

Read the full pregnancy detail

BreastfeedingInsufficient reliable information

Insufficient reliable information available; avoid using.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Jump to a section

Overview

Agar, also called agar-agar, is a gel-forming substance taken from the cell walls of certain red algae (seaweed). These seaweeds grow in oceans around the world, and agar is widely produced in Asia. It has been used in cooking and traditional preparations for a very long time.

In the kitchen, agar is best known as a vegetarian and vegan substitute for gelatin. It is used to make jellies, puddings, custards, and other desserts because it sets into a firm gel when cooled. Agar is also used in food manufacturing as a thickener and stabilizer, and in laboratories as a base for growing bacteria and other microbes.

As a supplement, agar is sold in powder, flake, bar, and capsule forms. People take it mainly for its high fiber content, often for digestive regularity or weight management.

How it works

Agar is made up mostly of two polysaccharides (long sugar chains) called agarose and agaropectin. These fibers are not broken down well by the human digestive system.

When agar reaches your stomach and intestines, it absorbs water and swells into a gel. This adds bulk and softness to stool, which is how bulk-forming laxatives generally help with regularity. The swelling may also create a feeling of fullness, which is the idea behind its use for appetite and weight control.

Most of these effects are explained by basic physical properties of fiber rather than by a specific drug-like action. Much of the research is laboratory-based, and human evidence for many proposed benefits is limited.

Effectiveness

Does Agar work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 3 uses evaluated

3 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

For Agar, current evidence isn’t strong enough to rate any specific use. The conditions it has been studied for are listed below.

Also studied for 3 conditions — evidence insufficient to rate

Insufficient Reliable Evidence To Rate Diabetes

Rating & evidence shown verbatim from Natural Medicines

Preliminary clinical research in obese patients with type 2 diabetes and impaired glucose tolerance shows that consuming seasoned agar gel (Slim Kanten, Choshiya) 180 grams daily in combination with a conventional Japanese diet for 12 weeks does not improve fasting plasma glucose or insulin resistance when compared to the conventional Japanese diet alone.

Sources Ref 30496

Insufficient Reliable Evidence To Rate Neonatal jaundice

Rating & evidence shown verbatim from Natural Medicines

The effects of agar on bilirubin levels in infants with neonatal jaundice are unclear, as results from clinical research are conflicting. Some preliminary clinical research shows that administering agar 0.6-2 grams daily for up to 5 days does not reduce bilirubin levels in infants with neonatal jaundice when compared to control. However, one clinical study shows that administering oral agar 500 mg four times daily reduces the time needed to lower bilirubin levels to 10 mg/dL or 15 mg/dL when compared with no treatment. Another clinical study in infants with baseline bilirubin levels between 10 mg/dL and 15 mg/dL shows that administering oral agar 300 mg/kg twice daily decreases bilirubin levels at 24 hours, 3 days, 5 days, and 7 days when compared with placebo.

Sources Ref 30491 Ref 30493 Ref 30504 Ref 30505 Ref 30507 Ref 30517 Ref 103245

Insufficient Reliable Evidence To Rate Obesity

Rating & evidence shown verbatim from Natural Medicines

Preliminary clinical research in obese patients with type 2 diabetes and impaired glucose tolerance shows that consuming seasoned agar gel (Slim Kanten, Choshiya) 180 grams daily in combination with a conventional Japanese diet for 12 weeks modestly reduces body weight and body mass index when compared with eating the conventional Japanese diet alone.

Sources Ref 30496

Source & disclaimer. Effectiveness ratings and evidence summaries are provided by Natural Medicines (Therapeutic Research Center) and shown as licensed. Where Natural Medicines hasn’t rated a use, HelloPharmacist’s pharmacists may add their own reviewed rating and evidence (each such entry is labeled). This is educational information, not medical advice — talk with your pharmacist or doctor before starting, stopping, or changing a supplement.

Safety & precautions

Agar is widely used in food and is generally recognized as safe when eaten in normal food amounts. The main safety concern with supplement doses is that, like other bulk-forming fibers, it can swell and potentially cause a blockage in the throat or intestines if it is not taken with enough liquid.

Always take agar supplements with a full glass of water. Do not take it dry or in very concentrated form. People with swallowing problems, a history of bowel obstruction, narrowing of the intestines, or trouble with constipation should talk to a doctor before using agar as a supplement.

Pregnancy: Agar eaten as a food is likely fine, but there is little data on concentrated supplement doses, so avoid these unless your doctor approves. Breastfeeding: Food amounts are likely fine, but supplement-level safety is not well studied, so use caution. When in doubt, choose the safer option and ask your pharmacist or doctor.

Side effects

For most people, agar in food amounts causes few problems. As a fiber, larger amounts may cause digestive side effects such as bloating, gas, cramping, or loose stools.

The most serious concern is choking or intestinal blockage if agar is swallowed without enough fluid or if it swells before it is fully eaten. This is rare but more likely with concentrated supplement forms. Allergic reactions are possible but uncommon.

If you have severe stomach pain, vomiting, trouble swallowing, or signs of a blockage after taking agar, stop using it and seek medical care.

Agar: Reported Adverse Effects

Documented safety reports on Agar from the evidence-graded Natural Medicines (TRC Healthcare) database, shown word-for-word from the licensed record.

Orally, no adverse effects have been reported; however, a thorough evaluation of safety outcomes has not been conducted. Rarely, phytobezoars and esophageal or bowel obstruction have been reported after ingestion of high-fiber foods, such as agar.

McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
Osada, T., Shibuya, T., Kodani, T., Beppu, K., Sakamoto, N., Nagahara, A., Ohkusa, T., Ogihara, T., and Watanabe, S. Obstructing small bowel bezoars due to an agar diet: diagnosis using double balloon enteroscopy. Intern.Med 2008;47(7):617-620.

Reports by condition

Bowel obstruction Gastrointestinal

Orally, phytobezoars, which are concentrations of fruit and vegetable fibers in the gastrointestinal tract, have been rarely reported following ingestion of high-fiber foods, such as agar. Esophageal or bowel obstruction has also been reported when agar is consumed without sufficient fluid intake.

Osada, T., Shibuya, T., Kodani, T., Beppu, K., Sakamoto, N., Nagahara, A., Ohkusa, T., Ogihara, T., and Watanabe, S. Obstructing small bowel bezoars due to an agar diet: diagnosis using double balloon enteroscopy. Intern.Med 2008;47(7):617-620.
McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.

Adverse-effects data: Natural Medicines, Therapeutic Research Center

Dosing

There is no official, well-established medical dose of agar. The amount used in cooking depends on the recipe, and supplement products vary widely.

If you use an agar supplement, follow the directions on the product label and take it with plenty of water. Because standardized dosing for health uses has not been established, it is best to start low and check with your pharmacist or doctor, especially if you have any digestive conditions or are pregnant or breastfeeding.

Pregnancy & Breastfeeding

Agar & Pregnancy

Insufficient reliable information

Insufficient reliable information available; avoid using.

Agar & Breastfeeding

Insufficient reliable information

Insufficient reliable information available; avoid using.

Pregnancy & lactation ratings: Natural Medicines, Therapeutic Research Center

References & further reading

The 13 references that drive our Agar monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
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.
Romagnoli, C., Polidori, G., Foschini, M., Cataldi, L., De, Turris P., Tortorolo, G., and Mastrangelo, R. Agar in the management of hyperbilirubinaemia in the premature baby. Arch.Dis.Child 1975;50(3):202-204. PubMed
Windorfer, A., Jr., Kunzer, W., Bolze, H., Ascher, K., Wilcken, F., and Hoehne, K. Studies on the effect of orally administered agar on the serum bilirubin level of premature infants and mature newborns. Acta Paediatr.Scand. 1975;64(5):699-702. PubMed
Maeda, H., Yamamoto, R., Hirao, K., and Tochikubo, O. Effects of agar (kanten) diet on obese patients with impaired glucose tolerance and type 2 diabetes. Diabetes Obes.Metab 2005;7(1):40-46.
Osada, T., Shibuya, T., Kodani, T., Beppu, K., Sakamoto, N., Nagahara, A., Ohkusa, T., Ogihara, T., and Watanabe, S. Obstructing small bowel bezoars due to an agar diet: diagnosis using double balloon enteroscopy. Intern.Med 2008;47(7):617-620. PubMed
Kemper, K., Horwitz, R. I., and McCarthy, P. Decreased neonatal serum bilirubin with plain agar: a meta-analysis. Pediatrics 1988;82(4):631-638. DOI
Meloni, T., Costa, S., Corti, R., and Cutillo, S. Agar in control of hyperbilirubinemia of full-term newborn infants with erythrocyte G-6-PD deficiency. Biol.Neonate 1978;34(5-6):295-298. PubMed
Maurer, H. M., Shumway, C. N., Draper, D. A., and Hossaini, A. A. Controlled trial comparing agar, intermittent phototherapy, and continuous phototherapy for reducing neonatal hyperbilirubinemia. J Pediatr. 1973;82(1):73-76.
Caglayan, S., Candemir, H., Aksit, S., Kansoy, S., Asik, S., and Yaprak, I. Superiority of oral agar and phototherapy combination in the treatment of neonatal hyperbilirubinemia. Pediatrics 1993;92(1):86-89. DOI
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
Abdel-Aziz Ali SMA, Mansour Galal S, Sror SM, Hussein O, Abd-El-Haseeb Ahmed AO, Hamed EA. Efficacy of oral agar in management of indirect hyperbilirubinemia in full-term neonates. J Matern Fetal Neonatal Med. 2020:1-6. PubMed

Keep reading

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.

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.

Brand directory

Brands that make products with Agar

46 brands in our database make a supplement containing Agar.

Atlantis Nutrition 11 products Bare Performance Nutrition 12 products Blaze 3 products Celebrate 44 products CON-CRET 12 products doTERRA 208 products Douglas Laboratories 3,067 products Dr. Mercola 590 products Fiber Choice 20 products Garden of Life Dr. Formulated 104 products Garden of Life Vitamin Code 184 products Genestra Brands 998 products Giant Sports 36 products GNC 848 products Hawaii Pharm 4,726 products Herbal Terra 3,138 products Host Defense Mushrooms 266 products KAL 204 products Keto Science 16 products Lifeable 41 products Lifeable Kids 28 products N by Nutrilite 15 products Natural Vitality 134 products Nature's Secret 76 products

Product directory

Supplement products with Agar

138 products in our database contain Agar. Open any to see its full ingredient list and every drug interaction we check.

Pharmacist Counseling Corner

Agar: Common Questions

What is Agar used for, and does it work?

People use Agar for a range of reasons, but according to the Natural Medicines database the current clinical evidence is insufficient to confirm it works for the specific conditions it has been studied for. See the graded list on this page, and talk to your pharmacist or doctor before relying on it for any condition.

Does Agar interact with prescription medications?

Yes. We list 2022 medications with a known interaction with Agar. Use the checker above to see how Agar interacts with a specific drug.

How are Agar interactions rated?

Each interaction is graded major, moderate, or minor based on how clinically significant it is and the strength of the evidence behind it. Major interactions are the most serious and are best avoided, or used only under close professional supervision.

Is it safe to take Agar with my medications?

It depends on the specific medication. Some combinations are fine, while others call for monitoring, timing changes, or should be avoided. Check your exact drug above and confirm with your pharmacist or doctor before starting, stopping, or changing anything.

Where does this Agar interaction information come from?

Our interaction data is built on the Natural Medicines database — an evidence-graded reference for vitamins, herbs, and supplements — and is reviewed by licensed HelloPharmacist pharmacists, who may add clinical context.

What is Agar used for?

Agar is mainly used as a plant-based substitute for gelatin in cooking and as a source of dietary fiber. Some people take it as a supplement for constipation or weight control, though strong human evidence for these uses is limited.

Is Agar vegan?

Yes. Agar comes from red seaweed, not animals, so it is a popular vegetarian and vegan alternative to gelatin, which is made from animal collagen.

Is Agar safe to eat?

Agar is generally considered safe in normal food amounts. With supplement doses, the main concern is swelling, so always take it with plenty of water to avoid choking or blockage.

Can Agar help with weight loss?

Agar is a fiber that swells and may help you feel full, which is why it is promoted for weight loss. However, the evidence that Agar alone leads to meaningful weight loss is weak.

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

Keep exploring

Products that contain Agar

A rotating sample of real supplements in our database that list Agar — open any to see its full ingredients and every drug interaction we check.

See all 138 products with Agar →

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Agar Drug Interactions, Uses, Effectiveness, Safety & More

Your Choice:

Drugs that interact with Agar

Don’t want to scroll the list? Just ask.

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Likelihood — How Well It’s Documented

Where This Data Comes From

The kinds of drugs Agar affects

Agar: Uses, Safety & Side Effects

Overview

How it works

Does Agar work?

Safety & precautions

Side effects

Agar: Reported Adverse Effects

Dosing

Agar & Pregnancy

Agar & Breastfeeding

References & further reading

Brands that make products with Agar

Supplement products with Agar

Agar: Common Questions

Related supplements & herbs

Products that contain Agar

Have a question about Agar?