Drug & supplement interaction

Collard + Metformin, Sitagliptin

Metformin, Sitagliptin brand names: Janumet, Janumet XR.

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

Collard has a moderate interaction with Metformin, Sitagliptin. In an animal study, an aqueous extract of collard leaves and stems has been shown to reduce glucose levels.

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

Collard and Metformin, Sitagliptin

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

Moderate

ANTIDIABETES DRUGS

Why this applies to Metformin, Sitagliptin

Metformin, Sitagliptin falls under ANTIDIABETES DRUGS — the group Collard interacts with.

In an animal study, an aqueous extract of collard leaves and stems has been shown to reduce glucose levels. Collard extract 60 mg/kg lowers blood glucose levels in a rat model of diabetes after both single- and multi-dose oral administration similarly to glibenclamide 5 mg/kg. Theoretically, collard extract might have additive effects when used concomitantly with antidiabetes drugs and may increase the risk of hypoglycemia. Monitor blood glucose levels closely. Dose adjustments may be necessary. Some antidiabetes drugs include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), chlorpropamide (Diabinese), glipizide (Glucotrol), and tolbutamide (Orinase).
Severity Moderate 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 gist: Janumet pairs two diabetes medicines, metformin and sitagliptin, and both work to bring your blood sugar down. Collard is really just a healthy leafy green, but in one animal study a concentrated extract of it also lowered blood sugar. So the concern is simply additive. If a strong collard extract nudges your sugar down on top of what Janumet already does, your levels could dip too low.

Honestly, this evidence is weak and only from rats, so eating collards in a normal meal is not something to worry about. Concentrated supplement doses are the question mark. Watch for shakiness, sweating, dizziness, or confusion, keep an eye on your readings, and check with your pharmacist before starting a collard supplement.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Amssayef A, Eddouks M. Antihyperglycemic Effect of the Moroccan Collard Green (Brassica oleracea var. viridis) in Streptozotocin-Induced Diabetic Rats. Endocr Metab Immune Disord Drug Targets 2020. 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

Collard Also Interacts With Other Medications

Collard has 85 moderate known drug interactions in our database — the Metformin, Sitagliptin one above is one of them. If you take anything else, check it against the full list below.

Moderate 85 No known interaction 2,745 (incl. Metformin, Sitagliptin)
Taking anything else?

Check Another of Your Medications Against Collard

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

Everything else you take

See Every Supplement That Interacts With Metformin, Sitagliptin

This page covers Collard only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metformin, Sitagliptin page lists 257 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Siberian Cocklebur (major), Acai (moderate), African Wild Potato (moderate) and Agaricus Mushroom (moderate).

By severity: 2 major · 217 moderate · 38 minor.

From our pharmacist’s overview on the Metformin, Sitagliptin page

“Many people prescribed metformin with sitagliptin (Janumet, Janumet XR) for type 2 diabetes also try herbs sold as blood sugar support, fenugreek among the most popular, and that habit is exactly where the risk on this page concentrates. Of 257 documented supplement interactions, 239 can push glucose in the same direction the medicatio…”

Reviewed by 2 · Jul 18, 2026

Open the Metformin, Sitagliptin interaction page

One more smart check

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

We hold 379 real supplement products containing Collard, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Collard. Your product may carry other ingredients that interact with Metformin, Sitagliptin too, on top of Collard — 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 Collard and Metformin, Sitagliptin 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 Collard
Top half

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

29 days ago today
Medication Metformin, Sitagliptin
Steady interest

#1,505 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 Collard

What is Collard?

  • General nutrition and vitamin source
  • Bone health
  • Heart health support
  • Digestive fiber
  • Antioxidant intake

Collard is a leafy green vegetable in the cabbage family that is rich in vitamins, minerals, and fiber, and is best thought of as a nutritious food rather than a medicine. Eating it as part of a balanced diet is healthy for most people, but there is little high-quality research on collard as a concentrated supplement. If you take blood thinners or have kidney concerns, talk with your pharmacist or doctor because of its vitamin K and oxalate content.

Read the full Collard monograph & all interactions
Keep checking

Other Drugs & Collard

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

0Major
85Moderate
0Minor
2,744No known interaction
85 Moderate 2,744 No interaction
Moderate

85 interactions

Showing 60 of 85 moderate interactions — see all 85 on the Collard page.

No interaction 2,744 drugs checked — show the list

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

Showing the 60 most looked-up of 2,744 medications checked with no known interaction — see the full Collard list.

See the full Collard interactions page
See every supplement checked against Metformin, Sitagliptin, 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
Collard monograph › Uses, safety, and every drug interaction in one place Metformin, Sitagliptin supplement interactions › Every supplement checked against Metformin, Sitagliptin, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Collard and Metformin, Sitagliptin Together: Common Questions

Can you take Collard with Metformin, Sitagliptin?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Collard and Metformin, Sitagliptin interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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.