Drug & supplement interaction

Blue-green Algae + Tadalafil

Tadalafil brand names: Cialis, Tadliq.

No Known Interaction

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Updated July 2026 · Pair last verified Sep 13, 2026

The bottom line No known interaction

We found no known interaction between Blue-green Algae and Tadalafil 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

Blue-green Algae and Tadalafil

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 Tadalafil and Blue-green Algae 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.

Blue-green Algae safety at a glance

Blue-green Algae overall Use caution Quality varies and some products can be contaminated with toxins or heavy metals.

Pregnancy Avoid Not enough safety data and contamination risk; best to avoid.

Breastfeeding Avoid Safety is unknown and contamination is a concern; best to avoid.

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

Still wondering about combining Tadalafil and Blue-green Algae? Ask Dr. Brian Staiger, PharmD, BCPS directly ›

How we checked

Why No Interaction Is Listed for Tadalafil

Interactions in our licensed database are recorded against drug classes, not just single drug names. Tadalafil is filed under 5 classifications — including phosphodiesterase-5 inhibitors, vasodilators, cytochrome p450 3a4 (cyp3a4) substrates. Blue-green Algae has documented interactions with 3 drug classes — the most serious being anticoagulant/antiplatelet drugs (moderate), antidiabetes drugs (moderate) and immunosuppressants (moderate) — and none of Tadalafil’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

Blue-green Algae Does Interact With Other Medications

Blue-green Algae has 327 moderate known drug interactions in our database — Tadalafil isn’t one of them. If you take anything else, check it against the full list below.

Moderate 327 No known interaction 2,503 (incl. Tadalafil)

Taking anything else?

Check Another of Your Medications Against Blue-green Algae

Covers the 2,830 medications we’ve checked against Blue-green Algae. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests Blue-green Algae and Tadalafil 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.

Stomach upset Additional detail
Blue-green Algae
“Orally, gastrointestinal complaints are amongst the most common adverse effects associated with spirulina blue-green algae, including nausea, vomiting, diarrhea, and abdominal cramps. Similarly, common adverse effects associated with the blue-green algae species Aphanizomenon flos-aquae are stomach upset, flatulence, diarrhea, and bloating.”

Blue-green Algae · Natural Medicines adverse-effect record, reported in diarrhea.
5 sources cited

19272. Katz M, Levine AA, Kol-Degani H, Kav-Venaki L. A compound herbal preparation (CHP) in the treatment of children with ADHD: a randomized controlled trial. J Atten Disord 2010;14:281-91. PubMed

75924. Halidou, Doudou M., Degbey, H., Daouda, H., Leveque, A., Donnen, P., Hennart, P., and Dramaix-Wilmet, M. [The effect of spiruline during nutritional rehabilitation: systematic review]. Rev.Epidemiol.Sante Publique 2008;56(6):425-431.

91713. Marles RJ, Barrett ML, Barnes J, et al. United States Pharmacopeia safety evaluation of spirulina. Crit Rev Food Sci Nutr 2011;51(7):593-604. PubMed

109969. Moradi S, Zobeiri M, Feizi A, Clark CCT, Entezari MH. The effects of spirulina (Arthrospira platensis) supplementation on anthropometric indices, blood pressure, sleep quality, mental health, fatigue status and quality of life in patients with ulcerative

14842. Vitale S, Miller NR, Mejico LJ, et al. A randomized, placebo-controlled, crossover clinical trial of super blue-green algae in patients with essential blepharospasm or Meige syndrome. Am J Ophthalmol 2004;138:18-32. PubMed
Tadalafil

Listed in the ADVERSE REACTIONS section of the FDA label for Tadalafil. Read the label on DailyMed ›
Headache reported in 11.1% of FDA reports for Tadalafil Additional detail

Blue-green Algae

“Orally, spirulina blue-green algae seem to be well tolerated.

Most Common Adverse Effects:

Orally: Abdominal cramps, bloating, diarrhea, dizziness, fatigue, flatulence, headache, nausea, and vomiting.”

Blue-green Algae · Natural Medicines adverse-effect record, reported in cluster headache.

Tadalafil

Listed in the ADVERSE REACTIONS section of the FDA label for Tadalafil, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›
Stomach pain Additional detail

Blue-green Algae

Recorded for Blue-green Algae in the same Natural Medicines adverse-effect record shown under Headache above.

Tadalafil

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

Reported for Blue-green Algae but not commonly for Tadalafil: an allergic reaction, muscle weakness, severe muscle breakdown and a severe allergic reaction.

Effects for Tadalafil come from the ADVERSE REACTIONS section of its FDA label; effects for Blue-green Algae come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 98,103 voluntary FDA FAERS reports for Tadalafil 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.

Overlapping uses

What Tadalafil Is Prescribed For, and What Blue-green Algae Has Been Studied For

These two come up together because they touch the same health topic — not because they do the same job. Tadalafil is a prescription medicine with approved uses on its FDA label. Blue-green Algae is a supplement: what follows is what researchers have looked at it for, and how strong that evidence is.

Tadalafil is prescribed for: Tadalafil tablets (including Cialis and generic tadalafil) are used to treat erectile dysfunction (ED), the symptoms of benign prostatic hyperplasia (BPH — an enlarged prostate), or both conditions together. When used with the drug finasteride to start BPH treatment, this combination is recommended for up to 26 weeks. Adcirca, Alyq (tablets), and Tadliq (oral suspension) are indicated specifically for pulmonary arterial hypertension (PAH — high blood pressure in the lungs), to improve the ability to exercise.

Blue-green Algae has been studied for:

Hypertension Natural Medicines rates the evidence for Blue-green Algae: Possibly Effective Read what the research shows

Blue-green Algae for hypertension

Oral blue-green algae seem to modestly reduce blood pressure in patients with hypertension.

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 Tadalafil on your own; if you are taking Blue-green Algae for the same health topic, tell your prescriber, especially if the medicine is being adjusted to a target.

From our Q&A

Questions About Blue-green Algae or Tadalafil

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Blue-green Algae or Tadalafil, 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 Tadalafil

This page covers Blue-green Algae only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Tadalafil page lists 144 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Mistletoe (major), Grapefruit (major), Hawthorn (major) and St. John's Wort (major).

By severity: 5 major · 98 moderate · 41 minor.

From our pharmacist’s overview on the Tadalafil page

“Grapefruit juice is the first thing to know about if you take tadalafil (Cialis, Tadliq). It blocks CYP3A4, the enzyme that clears the drug, so blood levels climb and side effects like a steep drop in blood pressure become more likely.”

Reviewed by 2 · Jul 18, 2026

Open the Tadalafil interaction page

One more smart check

Taking Blue-green Algae as Part of a Dietary Supplement Product? Check It for Interactions

We hold 3,180 real supplement products containing Blue-green Algae, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Blue-green Algae. Even though Blue-green Algae itself has no known interaction with Tadalafil, 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 Blue-green Algae and Tadalafil 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 Blue-green Algae

Top 10%

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

29 days ago today

Medication Tadalafil

Top 1%

#16 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 Blue-green Algae reference on this page ↓
Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Blue-green Algae and Tadalafil 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 Dr. Brian Staiger, PharmD, BCPS.

Supplement

About Blue-green Algae

What is Blue-green Algae?

General nutrition and energy
Antioxidant support
Cholesterol and metabolic health
Immune support
Weight management

Blue-green algae are nutrient-rich aquatic microorganisms (such as spirulina and Klamath Lake algae) taken as a supplement for energy, nutrition, and general wellness. Evidence for most health claims is limited, and some products can be contaminated with toxins or heavy metals, so quality testing matters. Talk to your pharmacist or doctor before using, especially during pregnancy or breastfeeding.

Whole dried microorganism (algae biomass) · Tablets, capsules, powder, flakes, and liquid extracts

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

Blue-green Algae: dosing

There is no official, standardized dose for blue-green algae, and the amount varies a lot from product to product. Different species and forms (tablet, powder, or liquid) also differ in strength.The safest approach is to follow the directions on the product label and not exceed them.

From our Blue-green Algae monograph — the full record covers uses, side effects and every documented interaction.

Read the full Blue-green Algae monograph & all interactions

Medication

About Tadalafil

What Is Tadalafil Used For?

Brand names: Cialis, Tadliq

Tadalafil tablets (including Cialis and generic tadalafil) are used to treat erectile dysfunction (ED), the symptoms of benign prostatic hyperplasia (BPH — an enlarged prostate), or both conditions together. When used with the drug finasteride to start BPH treatment, this combination is recommended for up to 26 weeks.

Adcirca, Alyq (tablets), and Tadliq (oral suspension) are indicated specifically for pulmonary arterial hypertension (PAH — high blood pressure in the lungs), to improve the ability to exercise.

Most-Reported Side Effects for Tadalafil

From FAERS, the FDA’s public side-effect reporting system (99,210 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Dyspnea 11,917 reports

Headache 10,982 reports

Diarrhea 8,020 reports

Nausea 6,697 reports

Fatigue 6,080 reports

See full Tadalafil drug information

Keep checking

Other Drugs & Blue-green Algae

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

0Major

327Moderate

0Minor

2,502No known interaction

327 Moderate 2,502 No interaction

Moderate

327 interactions

Showing 60 of 327 moderate interactions — see all 327 on the Blue-green Algae page.

No interaction 2,502 drugs checked — show the list

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

Showing the 60 most looked-up of 2,502 medications checked with no known interaction — see the full Blue-green Algae list.

See the full Blue-green Algae interactions page

See every supplement checked against Tadalafil, ranked by severity

Evidence & sources

Blue-green Algae References

The 22 references that drive our Blue-green Algae 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.

Jensen GS, Ginsberg DJ, Huerta P, et al. Consumption of Aphanizomenon flos-aquae has rapid effects on the circulation and function of immune cells in humans. A novel approach to nutritional mobilization of the immune system. JANA 2000;2:50-6.
Iwasa M, Yamamoto M, Tanaka Y, et al. Spirulina-associated hepatotoxicity. Am J Gastroenterol 2002;97:3212-13. PubMed
Hayashi O, Katoh T, Okuwaki Y. Enhancement of antibody production in mice by dietary Spirulina platensis. J Nutr Sci Vitaminol (Tokyo) 1994;40:431-41.. PubMed
Vitale S, Miller NR, Mejico LJ, et al. A randomized, placebo-controlled, crossover clinical trial of super blue-green algae in patients with essential blepharospasm or Meige syndrome. Am J Ophthalmol 2004;138:18-32. PubMed
Mani UV, Desai S, Iyer U. Studies on the long-term effect of spirulina supplementation on serum lipid profile and glycated proteins in NIDDM patients. J Nutraceut 2000;2(3):25-32. DOI
Chiu HF, Yang SP, Kuo YL, et al. Mechanisms involved in the antiplatelet effect of C-phycocyanin. Br J Nutr 2006;95:435-40. PubMed
Hsiao G, Chou PH, Shen MY, et al. C-phycocyanin, a very potent and novel platelet aggregation inhibitor from Spirulina platensis. J Agric Food Chem 2005;53:7734-40.
Katz M, Levine AA, Kol-Degani H, Kav-Venaki L. A compound herbal preparation (CHP) in the treatment of children with ADHD: a randomized controlled trial. J Atten Disord 2010;14:281-91. PubMed
Madhyastha, H. K., Radha, K. S., Sugiki, M., Omura, S., and Maruyama, M. Purification of c-phycocyanin from Spirulina fusiformis and its effect on the induction of urokinase-type plasminogen activator from calf pulmonary endothelial cells. Phytomedicine PubMed
Mazokopakis, E. E., Karefilakis, C. M., Tsartsalis, A. N., Milkas, A. N., and Ganotakis, E. S. Acute rhabdomyolysis caused by Spirulina (Arthrospira platensis). Phytomedicine. 2008;15(6-7):525-527. PubMed
Halidou, Doudou M., Degbey, H., Daouda, H., Leveque, A., Donnen, P., Hennart, P., and Dramaix-Wilmet, M. [The effect of spiruline during nutritional rehabilitation: systematic review]. Rev.Epidemiol.Sante Publique 2008;56(6):425-431.
Konno, T., Umeda, Y., Umeda, M., Kawachi, I., Oyake, M., and Fujita, N. [A case of inflammatory myopathy with widely skin rash following use of supplements containing Spirulina]. Rinsho Shinkeigaku 2011;51(5):330-333. PubMed
Le TM, Knulst AC, Röckmann H. Anaphylaxis to Spirulina confirmed by skin prick test with ingredients of Spirulina tablets. Food Chem Toxicol 2014;74:309-10. PubMed
Rzymski P, Niedzielski P, Kaczmarek N, Jurczak T, Klimaszyk P. The multidisciplinary approach to safety and toxicity assessment of microalgae-based food supplements following clinical cases of poisoning. Harmful Algae 2015;46:34-42. DOI
Petrus M, Culerrier R, Campistron M, et al. First case report of anaphylaxis to spirulin: identification of phycocyanin as responsible allergen. Allergy 2010;65(7):924-5. PubMed
Marles RJ, Barrett ML, Barnes J, et al. United States Pharmacopeia safety evaluation of spirulina. Crit Rev Food Sci Nutr 2011;51(7):593-604. PubMed
Majdoub H, Ben Mansour M, Chaubet F, et al. Anticoagulant activity of a sulfated polysaccharide from the green alga Arthrospira platensis. Biochim Biophys Acta 2009;1790(10):1377-81. PubMed
Cha BG, Kwak HW, Park AR, et al. Structural characteristics and biological performance of silk fibroin nanofiber containing microalgae spirulina extract. Biopolymers 2014;101(4):307-18. PubMed
Jensen GS, Drapeau C, Lenninger M, Benson KF. Clinical safety of a high dose of phycocyanin-enriched aqueous extract from Arthrospira (Spirulina) platensis: results from a randomized, double-Blind, placebo-controlled study with a focus on anticoagulant ac
Hamedifard Z, Milajerdi A, Reiner Z, Taghizadeh M, Kolahdooz F, Asemi Z. The effects of spirulina on glycemic control and serum lipoproteins in patients with metabolic syndrome and related disorders: A systematic review and meta-analysis of randomized con
Moradi S, Zobeiri M, Feizi A, Clark CCT, Entezari MH. The effects of spirulina (Arthrospira platensis) supplementation on anthropometric indices, blood pressure, sleep quality, mental health, fatigue status and quality of life in patients with ulcerative
Ghanbari F, Amerizadeh A, Behshood P, Moradi S, Asgary S. Effect of microalgae arthrospira on biomarkers of glycemic control and glucose metabolism: a systematic Review and meta-analysis. Curr Probl Cardiol 2022;47(10):100942. 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 Blue-green Algae and Tadalafil Together: Common Questions

Is it safe to take Blue-green Algae with Tadalafil?

We do not list a known interaction between Blue-green Algae and Tadalafil. 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 Blue-green Algae and Tadalafil have any of the same side effects?

Yes — our sources link each of them separately to 3 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.

Are Blue-green Algae and Tadalafil used for the same thing?

They overlap in purpose, which usually means the real question is whether you need both rather than whether they are safe together. This page lists the shared uses and how strong the evidence is for Blue-green Algae in each. That is a conversation for your prescriber, especially if Tadalafil is being adjusted to a target.

How was the Blue-green Algae and Tadalafil combination checked?

Interactions in our licensed database are recorded against drug classes. Tadalafil is filed under 5 classifications, and Blue-green Algae has documented interactions with 3 drug classes — none of Tadalafil'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 Blue-green Algae interact with any other medications?

Yes. Blue-green Algae has 327 documented drug interactions in our database — Tadalafil 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 Tadalafil interact with any supplements?

Yes. Tadalafil has documented interactions with 144 supplements in our database — Blue-green Algae is not one of them. The Tadalafil 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

Blue-green Algae monograph Uses, safety profile, and every drug interaction in one place Tadalafil drug information The full plain-English guide to this medication Tadalafil supplement interactions Every supplement checked against Tadalafil, 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 22 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Tadalafil and Blue-green Algae?

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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.