Drug & supplement interaction

D-mannose + Clemastine

Clemastine brand name: Tavist Allergy.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between D-mannose and Clemastine 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 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.

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Interaction report

D-mannose and Clemastine

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 Clemastine and D-mannose 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 D-mannose at all — not against Clemastine, 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.

D-mannose safety at a glance

D-mannose overall Use caution Generally well tolerated short-term, but high-quality long-term safety data are limited.
Pregnancy Use caution Not enough reliable safety data, so it is best to avoid unless your doctor advises otherwise.
Breastfeeding Use caution Safety while breastfeeding is not well studied, so caution is advised.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Clemastine and D-mannose? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

No Interaction Found — But Data Suggests D-mannose and Clemastine May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • Diarrhea / Nausea Additional detail

    D-mannose

    “Orally, D-mannose can cause loose stools, diarrhea, abdominal bloating, and nausea. In children, loose stools and abdominal bloating have been reported at D-mannose doses ranging from 100 mg/kg three times daily to 150 mg/kg five times daily. Diarrhea has been reported in adults taking D-mannose 2 grams daily for 6 months.”

    D-mannose · Natural Medicines adverse-effect record, reported in diarrhea.

    6 sources cited
    1. 13344. Westphal V, Kjaergaard S, Davis JA, et al. Genetic and metabolic analysis of the first adult with congenital disorder of glycosylation type Ib: long-term outcome and effects of mannose supplementation. Mol Genet Metab 2001;73:77-85. PubMed
    2. 91141. Kranjcec B, Papes D, Altarac S. D-mannose powder for prophylaxis of recurrent urinary tract infections in women: a randomized clinical trial. World J Urol. 2014 Feb;32(1):79-84.
    3. 100979. Harms HK, Zimmer KP, Kurnik K, Bertele-Harms RM, Weidinger S, Reiter K. Oral mannose therapy persistently corrects the severe clinical symptoms and biochemical abnormalities of phosphomannose isomerase deficiency. Acta Paediatr. 2002;91(10):1065-72. DOI
    4. 100981. . Damen G, de Klerk H, Huijmans J, den Hollander J, Sinaasappel M. Gastrointestinal and other clinical manifestations in 17 children with congenital disorders of glycosylation type Ia, Ib, and Ic. J Pediatr Gastroenterol Nutr. 2004;38(3):282-7. DOI
    5. 104209. Lenger SM, Bradley MS, Thomas DA, Bertolet MH, Lowder JL, Sutcliffe S. D-mannose vs other agents for recurrent urinary tract infection prevention in adult women: a systematic review and meta-analysis. Am J Obstet Gynecol. 2020;223(2):265.e1-265.e13. PubMed
    6. 100977. de Lonlay P, Seta N. The clinical spectrum of phosphomannose isomerase deficiency, with an evaluation of mannose treatment for CDG-Ib. Biochim Biophys Acta. 2009;1792(9):841-3. PubMed

    Clemastine

    Listed in the ADVERSE REACTIONS section of the FDA label for Clemastine. Read the label on DailyMed ›

Reported for D-mannose but not commonly for Clemastine: bloating or gas.

Effects for Clemastine come from the ADVERSE REACTIONS section of its FDA label; effects for D-mannose come from the Natural Medicines adverse-effect record, quoted above. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

From our Q&A

Questions About D-mannose or Clemastine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers D-mannose or Clemastine, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Clemastine

This page covers D-mannose only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Clemastine page lists 72 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Henbane (major), Scopolia (major), Alfalfa (moderate) and Angel's Trumpet (moderate).

By severity: 3 major · 57 moderate · 12 minor.

From our pharmacist’s overview on the Clemastine page

“Clemastine (Tavist Allergy) is an older, sedating antihistamine that already dries the mouth, blurs vision, and slows the gut, and that is exactly why this list earns real caution rather than a quick skim. Thirty of the 72 supplements on file pile the same drying, sedating anticholinergic load on top, and two of the three major-rated e…”

Reviewed by 2 · Jul 18, 2026

Open the Clemastine interaction page

How much people look this up

Where D-mannose and Clemastine 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 D-mannose
Steady interest

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

29 days ago today
Medication Clemastine
Steady interest

#2,051 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.

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 D-mannose reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The D-mannose and Clemastine 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.
Data structure & sourcing designed and verified by .
Supplement

About D-mannose

What is D-mannose?

D-mannose
  • Preventing urinary tract infections (UTIs)
  • Treating mild UTIs
  • Urinary tract health
  • Carbohydrate-deficient glycoprotein syndrome (a rare genetic condition)

D-mannose is a natural sugar most often used to help prevent urinary tract infections, especially those caused by E. coli. Early research is promising for prevention, but the evidence is still limited and it should not replace antibiotics for an active infection. Talk to your pharmacist or doctor before using it, particularly if you are pregnant, breastfeeding, or have diabetes.

Simple sugar (monosaccharide) derived from plants such as cranberries, apples, and other fruits and vegetables · Capsules, tablets, powder; often combined with cranberry

An interaction check asks whether these two react with each other — it does not ask whether D-mannose is a good idea for someone in your situation. Here is what our D-mannose record says about it on its own.

D-mannose: dosing

There is no official, standardized dose of D-mannose, and the amounts used in research have varied. Do not use D-mannose in place of prescribed antibiotics for an active infection.

From our D-mannose monograph — the full record covers uses, side effects and every documented interaction.

Read the full D-mannose monograph & all interactions
Medication

About Clemastine

What Is Clemastine Used For?

Brand name: Tavist Allergy

Clemastine treats symptoms of allergic rhinitis (hay fever and similar nasal allergies) — including sneezing, runny nose, itching, and watery eyes. The oral solution (Clemastine Fumarate syrup) is indicated for adults and children aged 6 through 12 years. The tablets (Clemastine Fumarate and Clemsza) are indicated for adults.

Clemastine also treats mild, uncomplicated allergic skin reactions — specifically urticaria (hives) and angioedema (swelling under the skin) — at the appropriate dosage level, in both the oral solution and tablet forms.

See full Clemastine drug information
Keep checking

Other Drugs & D-mannose

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full D-mannose list.

See the full D-mannose interactions page
See every supplement checked against Clemastine, ranked by severity
Evidence & sources

D-mannose References

The 6 references that drive our D-mannose 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.

  1. Westphal V, Kjaergaard S, Davis JA, et al. Genetic and metabolic analysis of the first adult with congenital disorder of glycosylation type Ib: long-term outcome and effects of mannose supplementation. Mol Genet Metab 2001;73:77-85. PubMed
  2. Kranjcec B, Papes D, Altarac S. D-mannose powder for prophylaxis of recurrent urinary tract infections in women: a randomized clinical trial. World J Urol. 2014 Feb;32(1):79-84.
  3. de Lonlay P, Seta N. The clinical spectrum of phosphomannose isomerase deficiency, with an evaluation of mannose treatment for CDG-Ib. Biochim Biophys Acta. 2009;1792(9):841-3. PubMed
  4. Harms HK, Zimmer KP, Kurnik K, Bertele-Harms RM, Weidinger S, Reiter K. Oral mannose therapy persistently corrects the severe clinical symptoms and biochemical abnormalities of phosphomannose isomerase deficiency. Acta Paediatr. 2002;91(10):1065-72. DOI
  5. . Damen G, de Klerk H, Huijmans J, den Hollander J, Sinaasappel M. Gastrointestinal and other clinical manifestations in 17 children with congenital disorders of glycosylation type Ia, Ib, and Ic. J Pediatr Gastroenterol Nutr. 2004;38(3):282-7. DOI
  6. Lenger SM, Bradley MS, Thomas DA, Bertolet MH, Lowder JL, Sutcliffe S. D-mannose vs other agents for recurrent urinary tract infection prevention in adult women: a systematic review and meta-analysis. Am J Obstet Gynecol. 2020;223(2):265.e1-265.e13. 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.

Pharmacist Counseling Corner

Taking D-mannose and Clemastine Together: Common Questions

Is it safe to take D-mannose with Clemastine?
We do not list a known interaction between D-mannose and Clemastine. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do D-mannose and Clemastine have any of the same side effects?
Yes — our sources link each of them separately to 2 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
Does Clemastine interact with any supplements?
Yes. Clemastine has documented interactions with 72 supplements in our database — D-mannose is not one of them. The Clemastine interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

D-mannose monograph Uses, safety profile, and every drug interaction in one place Clemastine drug information The full plain-English guide to this medication Clemastine supplement interactions Every supplement checked against Clemastine, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 6 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Clemastine and D-mannose?

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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.