Drug & supplement interaction

Chlorella + Orlistat

Orlistat brand names: Xenical, Alli.

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 Chlorella 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. 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

Chlorella 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 Chlorella 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.

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.

Chlorella safety at a glance

Chlorella overall Use caution Generally well tolerated short term, but product quality and purity vary widely.
Pregnancy Possibly Safe When used orally and appropriately in medicinal amounts for up to approximately 28 weeks. A commercially available chlorella supplement (Sun Chlorella A, Sun Ch... Read the full pregnancy detail
Breastfeeding Avoid Safety has not been established; avoid unless your doctor approves.

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Orlistat and Chlorella? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Orlistat

Interactions in our licensed database are recorded against drug classes, not just single drug names. Orlistat is filed under 2 classifications — including oral drugs. Chlorella has documented interactions with 2 drug classes — the most serious being photosensitizing drugs (moderate) and warfarin (coumadin) (moderate) — and none of Orlistat’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Chlorella Does Interact With Other Medications

Chlorella has 337 moderate known drug interactions in our database — Orlistat isn’t one of them. If you take anything else, check it against the full list below.

Moderate 337 No known interaction 2,493 (incl. Orlistat)
Taking anything else?

Check Another of Your Medications Against Chlorella

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

What to actually watch for

No Interaction Found — But Data Suggests Chlorella and Orlistat 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. 3 of them are worth acting on rather than waiting out — marked below.

  • Wheezing Worth acting on Additional detail

    Chlorella

    “Allergic reactions, including asthma and anaphylaxis, have been reported in people taking chlorella and in those preparing chlorella tablets.”

    Chlorella · Natural Medicines adverse-effect record, reported in asthma.

    3 sources cited
    1. 3900. Peirce A. The American Pharmaceutical Association Practical Guide to Natural Medicines. New York, NY: William Morrow and Co., 1999.
    2. 5847. Ng TP, Tan WC, Lee YK. Occupational asthma in a pharmacist induced by chlorella, a unicellular algae preparation. Resp Med 1994;88:555-7. PubMed
    3. 41827. Ng, T. P., Tan, W. C., and Lee, Y. K. Occupational asthma in a pharmacist induced by Chlorella, a unicellular algae preparation. Respir.Med. 1994;88(7):555-557. PubMed

    Orlistat

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

  • A severe allergic reaction / An allergic reaction Worth acting on Additional detail

    Chlorella

    “Orally, chlorella is generally well-tolerated.

    Most Common Adverse Effects:

    Orally: Allergic reactions, abdominal cramping, constipation, diarrhea, fatigue, flatus, nausea, photosensitivity, and stool discoloration.

    Serious Adverse Effects (Rare):

    Orally: Anaphylaxis.”

    Chlorella · Natural Medicines adverse-effect record, reported in constipation.

    Orlistat

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

  • Diarrhea / Stomach pain / Nausea reported in 7.6% of FDA reports for Orlistat Additional detail

    Chlorella

    “Orally, chlorella can cause diarrhea, abdominal cramping, flatus, and nausea, especially during the first two weeks of treatment. In one clinical trial, one out of 42 patients reported nausea and one reported diarrhea.”

    Chlorella · Natural Medicines adverse-effect record, reported in constipation.

    5 sources cited
    1. 5890. Merchant RE, Carmack CA, Wise CM. Nutritional supplementation with Chlorella pyrenoidosa for patients with fibromyalgia syndrome: a pilot study. Phytother Res 2000;14:167-73.
    2. 6804. Merchant RE, Rice CD, Young HF. Dietary Chlorella pyrenoidosa for patients with malignant glioma: effects on immunocompetence, quality of life, and survival. Phytother Res 1990;4:220-31.
    3. 92130. Azocar J, Diaz A. Efficacy and safety of chlorella supplementation in adults with chronic hepatitis C virus infection. World J Gastroenterol 2013;19(7):1085-90. PubMed
    4. 92132. Panahi Y, Badeli R, Karami GR, Badeli Z, Sahebkar A. A randomized controlled trial of 6-week Chlorella vulgaris supplementation in patients with major depressive disorder. Complement Ther Med 2015;23(4):598-602. PubMed
    5. 95013. Nakano S, Takekoshi H, Nakano M. Chlorella pyrenoidosa supplementation reduces the risk of anemia, proteinuria and edema in pregnant women. Plant Foods Hum Nutr 2010;65(1):25-30. PubMed

    Orlistat

    Listed in the ADVERSE REACTIONS section of the FDA label for Orlistat, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • Tiredness Additional detail

    Chlorella

    “Orally, manganese (Mn)-induced parkinsonism has been reported after long-term consumption of chlorella extract. In this case, a patient on maintenance hemodialysis reported gait disturbance, dysarthria, elevated serum and cerebrospinal fluid manganese levels, and abnormal magnetic resonance imaging (MRI) findings of the brain.”

    Chlorella · Natural Medicines adverse-effect record, reported in fatigue.

    2 sources cited
    1. 41817. Ohtake, T., Negishi, K., Okamoto, K., Oka, M., Maesato, K., Moriya, H., and Kobayashi, S. Manganese-induced Parkinsonism in a patient undergoing maintenance hemodialysis. Am J Kidney Dis 2005;46(4):749-753. PubMed
    2. 10388. Halperin SA, Smith B, Nolan C, et al. Safety and immunoenhancing effect of a Chlorella-derived dietary supplement in healthy adults undergoing influenza vaccination: randomized, double-blind, placebo-controlled trial. CMAJ 2003;169:111-7..

    Orlistat

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

Reported for Chlorella but not commonly for Orlistat: unsteadiness, sun sensitivity, a low platelet count and constipation.

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

Special populations

Chlorella in Pregnancy & Breastfeeding

Pregnancy Possibly Safe

When used orally and appropriately in medicinal amounts for up to approximately 28 weeks. A commercially available chlorella supplement (Sun Chlorella A, Sun Chlorella Corp.) has been safely used in doses of 6 grams daily, starting during the 12-18th week of gestation and continuing until delivery.

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.© 2026 Therapeutic Research Center

From our Q&A

Questions About Chlorella or Orlistat

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Chlorella or Orlistat, 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 Orlistat

This page covers Chlorella 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 Chlorella as Part of a Dietary Supplement Product? Check It for Interactions

We hold 3,341 real supplement products containing Chlorella, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Chlorella. Even though Chlorella 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 Chlorella 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 Chlorella
Top 10%

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

29 days ago today
Medication Orlistat
Top 10%

#239 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 Chlorella reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Chlorella and Orlistat records this page draws on were last updated July 11, 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 Chlorella

What is Chlorella?

Chlorella
  • General nutrition and 'detox' support
  • Immune support
  • Liver and kidney support
  • Antioxidant and anti-inflammatory support
  • Cholesterol and heart health

Chlorella is a nutrient-rich freshwater green algae taken as a supplement for general wellness, immune support, and 'detox.' Some small studies suggest possible benefits for cholesterol, blood pressure, and immune markers, but the overall evidence is limited and not strong. It is generally well tolerated, but quality varies and it should be avoided during pregnancy and breastfeeding unless a doctor approves.

Chlorella vulgaris · Chlorellaceae · Whole dried algae cells · Tablets, capsules, powder, extract, and liquid

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

Chlorella: dosing

There is no official, standardized dose for chlorella. Studies have used a wide range of amounts, and products differ in strength and quality, so there is no one 'correct' dose.The best approach is to follow the directions on the product label and start with a lower amount to see how your body reacts.

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

Read the full Chlorella 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 & Chlorella

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

0Major
337Moderate
0Minor
2,492No known interaction
337 Moderate 2,492 No interaction
Moderate

337 interactions

Showing 60 of 337 moderate interactions — see all 337 on the Chlorella page.

No interaction 2,492 drugs checked — show the list

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

Showing the 60 most looked-up of 2,492 medications checked with no known interaction — see the full Chlorella list.

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

Chlorella References

The 13 references that drive our Chlorella 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. Peirce A. The American Pharmaceutical Association Practical Guide to Natural Medicines. New York, NY: William Morrow and Co., 1999.
  2. Ng TP, Tan WC, Lee YK. Occupational asthma in a pharmacist induced by chlorella, a unicellular algae preparation. Resp Med 1994;88:555-7. PubMed
  3. Jitsukawa K, Suizu R, Hidano A. Chlorella photosensitization. New phytophotodermatosis. Int J Dermatol 1984;23:263-8. PubMed
  4. Merchant RE, Carmack CA, Wise CM. Nutritional supplementation with Chlorella pyrenoidosa for patients with fibromyalgia syndrome: a pilot study. Phytother Res 2000;14:167-73.
  5. Merchant RE, Rice CD, Young HF. Dietary Chlorella pyrenoidosa for patients with malignant glioma: effects on immunocompetence, quality of life, and survival. Phytother Res 1990;4:220-31.
  6. Halperin SA, Smith B, Nolan C, et al. Safety and immunoenhancing effect of a Chlorella-derived dietary supplement in healthy adults undergoing influenza vaccination: randomized, double-blind, placebo-controlled trial. CMAJ 2003;169:111-7..
  7. Ohtake, T., Negishi, K., Okamoto, K., Oka, M., Maesato, K., Moriya, H., and Kobayashi, S. Manganese-induced Parkinsonism in a patient undergoing maintenance hemodialysis. Am J Kidney Dis 2005;46(4):749-753. PubMed
  8. Ng, T. P., Tan, W. C., and Lee, Y. K. Occupational asthma in a pharmacist induced by Chlorella, a unicellular algae preparation. Respir.Med. 1994;88(7):555-557. PubMed
  9. Ohkawa, S., Yoneda, Y., Ohsumi, Y., and Tabuchi, M. [Warfarin therapy and chlorella]. Rinsho Shinkeigaku 1995;35(7):806-807.
  10. Azocar J, Diaz A. Efficacy and safety of chlorella supplementation in adults with chronic hepatitis C virus infection. World J Gastroenterol 2013;19(7):1085-90. PubMed
  11. Panahi Y, Badeli R, Karami GR, Badeli Z, Sahebkar A. A randomized controlled trial of 6-week Chlorella vulgaris supplementation in patients with major depressive disorder. Complement Ther Med 2015;23(4):598-602. PubMed
  12. Nakano S, Takekoshi H, Nakano M. Chlorella pyrenoidosa supplementation reduces the risk of anemia, proteinuria and edema in pregnant women. Plant Foods Hum Nutr 2010;65(1):25-30. PubMed
  13. Yavasoglu I, Turgutkaya A, Bolaman Z. Chlorella-induced thrombocytopenia. Sao Paulo Med J 2018;136(6):602-3. 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 Chlorella and Orlistat Together: Common Questions

Is it safe to take Chlorella with Orlistat?
We do not list a known interaction between Chlorella 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.
Do Chlorella and Orlistat have any of the same side effects?
Yes — our sources link each of them separately to 7 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.
How was the Chlorella and Orlistat combination checked?
Interactions in our licensed database are recorded against drug classes. Orlistat is filed under 2 classifications, and Chlorella has documented interactions with 2 drug classes — none of Orlistat's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Chlorella interact with any other medications?
Yes. Chlorella has 337 documented drug interactions in our database — Orlistat is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Orlistat interact with any supplements?
Yes. Orlistat has documented interactions with 18 supplements in our database — Chlorella 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

Chlorella 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 13 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Orlistat and Chlorella?

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.