Drug & supplement interaction

Ornithine + Orlistat

Orlistat brand names: Xenical, Alli.

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

We found no known interaction between Ornithine and Orlistat 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.

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Interaction report

Ornithine and Orlistat

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 Orlistat and Ornithine 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 Ornithine at all — not against Orlistat, 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.

Ornithine safety at a glance

Ornithine overall Use caution Generally well tolerated short-term, but long-term safety is not well studied.
Pregnancy Avoid Not enough safety data; best to avoid during pregnancy.
Breastfeeding Avoid Not enough safety data; best to avoid while breastfeeding.

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

Still wondering about combining Orlistat and Ornithine? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Orlistat’s Own FDA Label Lists

This is not an interaction — none of it involves Ornithine. These are the most notable effects listed in the ADVERSE REACTIONS section of Orlistat’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both. 10 of them are worth acting on rather than waiting out — marked below.

  • Bleeding in the gut Worth acting on
  • Low blood sugar Worth acting on
  • Pancreatitis Worth acting on
  • Wheezing Worth acting on
  • Low mood Worth acting on
  • A severe allergic reaction Worth acting on
  • Hives Worth acting on
  • Liver problems Worth acting on
  • Bleeding or bruising Worth acting on
  • A higher chance of infection Worth acting on

Showing the 10 most notable of 28 label-listed effects — ranked by how unusual each one is across medicines generally, with serious effects weighted up.

From the ADVERSE REACTIONS section of the FDA label for Orlistat. Read the label on DailyMed › Where a percentage is shown, it is the share of 25,755 voluntary FDA FAERS reports for Orlistat that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Ornithine’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Ornithine side to compare — that is a limit of the record, not a statement that Ornithine has no side effects.

Everything else you take

See Every Supplement That Interacts With Orlistat

This page covers Ornithine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Orlistat 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), Fish Oil (moderate) and Glucomannan (moderate).

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

From our pharmacist’s overview on the Orlistat page

“People who take Orlistat (Xenical, Alli) for weight loss often browse the very supplement aisle where fiber products and fish oil sit, and both show up on this page, so it deserves genuine attention before you mix anything in. Nearly all 18 ingredients on file can change how oral medications absorb from the gut, and the single major-ra…”

Reviewed by 2 · Jul 18, 2026

Open the Orlistat interaction page

One more smart check

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

We hold 751 real supplement products containing Ornithine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Ornithine. Even though Ornithine itself has no known interaction with Orlistat, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Ornithine and Orlistat 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 Ornithine
Top 25%

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

29 days ago today
Medication Orlistat
Top 25%

#454 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. Ornithine is not yet covered by that licensed database, so its write-up cites publicly available medical sources directly (see the references below).
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Ornithine reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Ornithine and Orlistat records this page draws on were last updated June 22, 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 Ornithine

What is Ornithine?

  • Athletic performance and recovery
  • Reducing fatigue
  • Sleep and stress support
  • Liver and ammonia metabolism support
  • Wound healing

Ornithine is a non-essential amino acid your body makes naturally as part of the urea cycle, which helps remove ammonia. It is sold as a supplement for fatigue, exercise recovery, and sleep, but human evidence is limited and mixed. Talk to your pharmacist or doctor before using it, especially if you have a medical condition.

Amino acid (not a plant part) · Capsules, tablets, powder, often as L-ornithine or ornithine alpha-ketoglutarate (OKG)

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

Ornithine: dosing

There is no official, standardized dose of ornithine for any supplement use. Amounts used in studies have varied widely, and there is not enough strong evidence to recommend a specific dose.The safest approach is to follow the directions on the product label and not exceed them.

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

Read the full Ornithine monograph & all interactions
Medication

About Orlistat

What Is Orlistat Used For?

Brand names: Xenical, Alli

Xenical and prescription-strength orlistat are approved to help obese adults lose weight and keep it off when used with a reduced-calorie diet. They are intended for people with a body mass index (BMI) of 30 or higher, or 27 or higher if other risk factors such as high blood pressure, diabetes, or dyslipidemia (abnormal cholesterol or fat levels in the blood) are present.

Alli is the over-the-counter version, approved for weight loss in overweight adults 18 and older when used with a reduced-calorie, low-fat diet and exercise program.

Most-Reported Side Effects for Orlistat

From FAERS, the FDA’s public side-effect reporting system (25,755 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Rectal discharge 2,434 reports
Gastrointestinal disorder 2,186 reports
Constipation 1,991 reports
Diarrhea 1,960 reports
Weight increased 1,944 reports
See full Orlistat drug information
Keep checking

Other Drugs & Ornithine

Browse every other medication we’ve checked against Ornithine — 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 Ornithine 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 Ornithine list.

See the full Ornithine interactions page
See every supplement checked against Orlistat, ranked by severity
Evidence & sources

Ornithine References

The 1 sources that drive our Ornithine monograph — publicly available pages from reputable medical and government organizations. Every link was verified to work before publishing. Ornithine is not covered by the licensed Natural Medicines interaction database, so its page cites these public sources directly.

  1. Dietary Supplements: What You Need to Know — NIH Office of Dietary Supplements Source

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 Ornithine and Orlistat Together: Common Questions

Is it safe to take Ornithine with Orlistat?
We do not list a known interaction between Ornithine and Orlistat. 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.
Does Orlistat interact with any supplements?
Yes. Orlistat has documented interactions with 18 supplements in our database — Ornithine is not one of them. The Orlistat 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

Ornithine monograph Uses, safety profile, and every drug interaction in one place Orlistat drug information The full plain-English guide to this medication Orlistat supplement interactions Every supplement checked against Orlistat, 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 1 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Orlistat and Ornithine?

Our pharmacists answer your medication & supplement questions — free.

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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.