Fructo-oligosaccharides (fos) + Methylnaltrexone
Methylnaltrexone brand name: Relistor.
We found no known interaction between Fructo-oligosaccharides (fos) and Methylnaltrexone in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the label for Methylnaltrexone states a food rule worth keeping to, and the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.
Fructo-oligosaccharides (fos) and Methylnaltrexone
We checked these two against our interaction database. Here is what we found.
No Known Interaction Found
We did not find a documented interaction between Methylnaltrexone and Fructo-oligosaccharides (fos) in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.
Worth understanding: our licensed dataset holds no drug-interaction record for Fructo-oligosaccharides (fos) at all — not against Methylnaltrexone, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.
If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.
Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.
Fructo-oligosaccharides (fos) safety at a glance
Safety guidance is general; always confirm with your pharmacist or doctor for your situation.
Some Methylnaltrexone Products Have a Food Rule — Fructo-oligosaccharides (fos) Should Not Break It
At least one FDA label for a product containing Methylnaltrexone says to take it on an empty stomach. Most supplements — Fructo-oligosaccharides (fos) included — are taken with a meal, so the easy mistake is swallowing both together at breakfast. Where that rule applies, keep Methylnaltrexone on its own and move Fructo-oligosaccharides (fos) to a meal later in the day.
This may not be true of your version. Food instructions belong to the product, not the ingredient: two Methylnaltrexone products can carry different directions, and extended-release forms often differ from immediate-release ones. The label we read is quoted below — check the directions on your own box or bottle, or ask your pharmacist, for how to take the exact product you were given.
o In patients with chronic non-cancer pain and OIC, take RELISTOR tablets with water on an empty stomach at least 30 minutes before the first meal of the day.
From the Dosage and Administration section of the FDA label we read for Methylnaltrexone — where that label names a specific product, the instruction is that product's. Read the label on DailyMed ›
A food rule is not an interaction — it is about how much of the medicine you absorb. The directions that came with your own product, and your pharmacist, outrank anything on this page.
What Methylnaltrexone Is Prescribed For, and What Fructo-oligosaccharides (fos) Has Been Studied For
These two come up together because they touch the same health topic — not because they do the same job. Methylnaltrexone is a prescription medicine with approved uses on its FDA label. Fructo-oligosaccharides (fos) is a supplement: what follows is what researchers have looked at it for, and how strong that evidence is.
Methylnaltrexone is prescribed for: Methylnaltrexone, sold as Relistor, treats opioid-induced constipation (OIC) — constipation caused by opioid pain medications. Both Relistor tablets and Relistor injection are approved for adults with chronic non-cancer pain, including those with pain related to a prior cancer or its treatment who do not need frequent opioid dose increases. Relistor injection is also approved for adults with advanced illness or active cancer pain who require increasing opioid doses as part of palliative care.
Fructo-oligosaccharides (fos) has been studied for:
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Constipation studied, not established Fructo-oligosaccharides (fos) has been studied for this. Natural Medicines rates the evidence: Insufficient Reliable Evidence To Rate Read what the research shows
Fructo-oligosaccharides (fos) for constipation
Small clinical studies suggest that oral FOS may modestly improve symptoms in patients with constipation when used in combination with probiotics. The benefits of FOS when used alone are unclear.
Effectiveness ratings and the research summaries above are the verbatim record from the Natural Medicines database, which grades evidence from “Effective” down to “Insufficient Reliable Evidence To Rate”. A rating below the top of that scale means researchers have looked at it — not that it works, and never that it can stand in for a prescribed medicine. Do not stop or replace Methylnaltrexone on your own; if you are taking Fructo-oligosaccharides (fos) for the same health topic, tell your prescriber, especially if the medicine is being adjusted to a target.
See Every Supplement That Interacts With Methylnaltrexone
This page covers Fructo-oligosaccharides (fos) only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Methylnaltrexone page lists 3 supplements it has a documented interaction with, worst first, each one explained.
The most serious there right now: Fever Bark (moderate), Iboga (moderate) and Yohimbe (moderate).
By severity: 3 moderate.
From our pharmacist’s overview on the Methylnaltrexone page
“If you take methylnaltrexone (Relistor) for opioid-induced constipation, the supplement list to know is short: three ingredients, all rated moderate, none major. Yohimbe, fever bark, and iboga are all cleared by the same liver enzyme, CYP2D6, and methylnaltrexone can slow that enzyme, letting their active compounds build up in your blood.”
Reviewed by 2 · Jul 18, 2026
Taking Fructo-oligosaccharides (fos) as Part of a Dietary Supplement Product? Check It for Interactions
We hold 1,251 real supplement products containing Fructo-oligosaccharides (fos), each one broken down to its full ingredient list — and combination products often carry several ingredients besides Fructo-oligosaccharides (fos). Even though Fructo-oligosaccharides (fos) itself has no known interaction with Methylnaltrexone, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:
Where Fructo-oligosaccharides (fos) and Methylnaltrexone 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.
#228 of 1,452 supplements looked up here in the last 7 days
#2,090 of 2,830 medications looked up here in the last 7 days
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.
Where does our data come from?
- Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
- Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Fructo-oligosaccharides (fos) reference on this page ↓
- Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Fructo-oligosaccharides (fos) and Methylnaltrexone records this page draws on were last updated July 10, 2026.
- What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
About Fructo-oligosaccharides (fos)
What is Fructo-oligosaccharides (fos)?
- Digestive and gut health
- Prebiotic to support good bacteria
- Constipation relief
- Calcium absorption support
- Blood sugar and appetite support
Fructo-oligosaccharides (FOS) are a type of soluble fiber that acts as a prebiotic, meaning they feed the helpful bacteria in your gut. They are generally considered safe for most people in normal food amounts, but higher doses commonly cause gas and bloating. Evidence for many health claims is still limited, so talk with your pharmacist or doctor before using FOS supplements.
Carbohydrate fibers extracted from plants such as chicory root, or made by enzymatic processing of sugars · Powders, capsules, syrups, added to foods and infant formulas, and combined with probiotics in synbiotic products
An interaction check asks whether these two react with each other — it does not ask whether Fructo-oligosaccharides (fos) is a good idea for someone in your situation. Here is what our Fructo-oligosaccharides (fos) record says about it on its own.
Fructo-oligosaccharides (fos): dosing
There is no single official or standardized dose of FOS. Amounts used in studies and products vary widely, often given as a few grams of fiber per day.Because higher amounts increase the risk of gas and bloating, it is best to start low and increase gradually if needed.
From our Fructo-oligosaccharides (fos) monograph — the full record covers uses, side effects and every documented interaction.
About Methylnaltrexone
What Is Methylnaltrexone Used For?
Brand name: Relistor
Methylnaltrexone, sold as Relistor, treats opioid-induced constipation (OIC) — constipation caused by opioid pain medications. Both Relistor tablets and Relistor injection are approved for adults with chronic non-cancer pain, including those with pain related to a prior cancer or its treatment who do not need frequent opioid dose increases.
Relistor injection is also approved for adults with advanced illness or active cancer pain who require increasing opioid doses as part of palliative care.
Other Drugs & Fructo-oligosaccharides (fos)
Browse every other medication we’ve checked against Fructo-oligosaccharides (fos) — both the ones with a known interaction and the ones without. Select any drug for the full detail.
No drugs match “”.
No interaction 2,829 drugs checked — show the list
We also checked Fructo-oligosaccharides (fos) against these medications and found no known interaction in our sources. Open any page to confirm.
- Apixaban ›
- Levothyroxine ›
- Amlodipine ›
- Methylphenidate ›
- Warfarin ›
- Sertraline ›
- Testosterone ›
- Ivermectin ›
- Losartan Potassium ›
- Abemaciclib ›
- Aspirin ›
- Acetaminophen ›
- Metoprolol ›
- Rosuvastatin ›
- Rivaroxaban ›
- Escitalopram ›
- Clopidogrel ›
- Atorvastatin ›
- Docusate ›
- Tadalafil ›
- Tirzepatide ›
- Methamphetamine ›
- Ibuprofen ›
- Warfarin Sodium ›
- Valacyclovir ›
- Hydroxyurea ›
- Sumatriptan ›
- Semaglutide ›
- Prednisone ›
- Propranolol ›
- Lisdexamfetamine ›
- Amitriptyline ›
- Metformin ›
- Amoxicillin ›
- Lisinopril ›
- Isotretinoin ›
- Amlodipine Besylate ›
- Bendamustine ›
- Methotrexate ›
- Bupropion ›
- Amphetamine ›
- Fluoxetine ›
- Doxycycline ›
- Azithromycin ›
- Acyclovir ›
- Pregabalin ›
- Lamotrigine ›
- Dextroamphetamine ›
- Gabapentin ›
- Acetaminophen, Codeine ›
- Levothyroxine, Liothyronine ›
- Clonazepam ›
- Quetiapine ›
- Naproxen ›
- Omeprazole ›
- Letrozole ›
- Duloxetine ›
- Methylene Blue ›
- Buspirone ›
- Citalopram ›
Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Fructo-oligosaccharides (fos) list.
Fructo-oligosaccharides (fos) References
The 6 references that drive our Fructo-oligosaccharides (fos) 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.
- Briet F, et al. Symptomatic response to varying levels of fructo-oligosaccharides consumed occasionally or regularly. Eur J Clin Nutr 1995;49:501-7.
- Bouhnik Y, Vahedi K, Achour L, et al. Short-chain fructo-oligosaccharide administration dose-dependently increases fecal bifidobacteria in healthy humans. J Nutr 1999;129:113-6. PubMed
- Cummings JH, Macfarlane GT, Englyst HN. Prebiotic digestion and fermentation. Am J Clin Nutr 2001;73:415S-420S. PubMed
- Souza DDS, Tahan S, Weber TK, Araujo-Filho HB, de Morais MB. Randomized, double-blind, placebo-controlled parallel clinical trial assessing the effect of fructooligosaccharides in infants with constipation. Nutrients. 2018;10(11). pii: E1602. PubMed
- Andermann TM, Fouladi F, Tamburini FB, et al. A Fructo-Oligosaccharide Prebiotic Is Well Tolerated in Adults Undergoing Allogeneic Hematopoietic Stem Cell Transplantation: A Phase I Dose-Escalation Trial. Transplant Cell Ther 2021;27(11):932. PubMed
- Dou Y, Yu X, Luo Y, Chen B, Ma D, Zhu J. Effect of Fructooligosaccharides Supplementation on the Gut Microbiota in Human: A Systematic Review and Meta-Analysis. Nutrients 2022;14(16):3298. PubMed
Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.
Taking Fructo-oligosaccharides (fos) and Methylnaltrexone Together: Common Questions
Is it safe to take Fructo-oligosaccharides (fos) with Methylnaltrexone?
Do Fructo-oligosaccharides (fos) and Methylnaltrexone have any of the same side effects?
Should I take Fructo-oligosaccharides (fos) and Methylnaltrexone at the same time of day?
Are Fructo-oligosaccharides (fos) and Methylnaltrexone used for the same thing?
Does Methylnaltrexone interact with any supplements?
Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy
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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.