Drug & supplement interaction

Tribulus + Guanfacine

Guanfacine brand name: Tenex.

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

Tribulus has a moderate interaction with Guanfacine. Theoretically, taking tribulus with antihypertensive drugs might increase the risk of hypotension.

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

Tribulus and Guanfacine

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

Moderate

ANTIHYPERTENSIVE DRUGS

Why this applies to Guanfacine

Guanfacine falls under ANTIHYPERTENSIVE DRUGS — the group Tribulus interacts with.

Theoretically, taking tribulus with antihypertensive drugs might increase the risk of hypotension.
Animal research shows that tribulus can lower blood pressure by inhibiting angiotensin-converting enzyme (ACE). Tribulus has also demonstrated hypotensive effects in pre-hypertensive adults.
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 simple version: guanfacine already lowers your blood pressure by calming the signals that tighten your blood vessels and speed up your heart. Tribulus may have a mild blood-pressure-lowering effect of its own, so stacking the two could push your numbers down a little more than expected.

If that happens, you might feel the kinds of things guanfacine can already cause, like dizziness, lightheadedness when you stand up, tiredness, or a slow heartbeat. I'll be honest with you though, this concern is mostly theoretical, coming from animal studies and a small signal in pre-hypertensive folks, so it isn't a strong or proven interaction. Still, it's worth mentioning to your pharmacist or doctor before adding Tribulus, especially if your blood pressure tends to run low.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Sharifi AM, Darabi R, Akbarloo N. Study of antihypertensive mechanism of Tribulus terrestris in 2K1C hypertensive rats: role of tissue ACE activity. Life Sci 2003;73:2963-71. PubMed
  2. Siddiqui MA, Itrat M, Mobeen A, Khan MI. Efficacy of khar-i-khasak (Tribulus terrestris Linn.) in prehypertension: a randomized, double-blind, placebo-controlled trial. J Complement Integr Med. 2021.

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

Tribulus Also Interacts With Other Medications

Tribulus has 258 moderate known drug interactions in our database — the Guanfacine one above is one of them. If you take anything else, check it against the full list below.

Moderate 258 No known interaction 2,572 (incl. Guanfacine)
Taking anything else?

Check Another of Your Medications Against Tribulus

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

From our Q&A

Questions About Tribulus or Guanfacine

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

This page covers Tribulus only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Guanfacine page lists 136 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), American Mistletoe (major), Tyramine (major) and Adrafinil (moderate).

By severity: 4 major · 111 moderate · 21 minor.

Open the Guanfacine interaction page

One more smart check

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

We hold 1,680 real supplement products containing Tribulus, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Tribulus. Your product may carry other ingredients that interact with Guanfacine too, on top of Tribulus — 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 Tribulus and Guanfacine 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 Tribulus
Top 10%

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

29 days ago today
Medication Guanfacine
Top half

#747 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 Tribulus

What is Tribulus?

Tribulus
  • Low libido and sexual function
  • Athletic performance and muscle building
  • Testosterone support
  • Male and female fertility
  • General 'vitality' or wellness

Tribulus is a plant supplement most often marketed to boost libido, testosterone, and athletic performance, but the human evidence behind these claims is weak and inconsistent. It is generally well tolerated by healthy adults in the short term, but it should be avoided during pregnancy and breastfeeding and discussed with your pharmacist or doctor before use.

Read the full Tribulus monograph & all interactions
Medication

About Guanfacine

What Is Guanfacine Used For?

Brand name: Tenex

Guanfacine immediate-release tablets (Guanfacine, Guanfacine Hydrochloride) are used to manage high blood pressure (hypertension). They can be used alone or together with other blood pressure medicines, especially thiazide-type diuretics (water pills).

Guanfacine extended-release tablets — sold as Guanfacine ER, Guanfacine extended-release, and Intuniv — are approved for the treatment of ADHD in children and adolescents ages 6 to 17. They can be used on their own (monotherapy) or alongside stimulant ADHD medications as add-on therapy.

See full Guanfacine drug information
Keep checking

Other Drugs & Tribulus

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

0Major
258Moderate
0Minor
2,571No known interaction
258 Moderate 2,571 No interaction
Moderate

258 interactions

Showing 60 of 258 moderate interactions — see all 258 on the Tribulus page.

No interaction 2,571 drugs checked — show the list

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

Showing the 60 most looked-up of 2,571 medications checked with no known interaction — see the full Tribulus list.

See the full Tribulus interactions page
See every supplement checked against Guanfacine, 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
Tribulus monograph › Uses, safety, and every drug interaction in one place Guanfacine supplement interactions › Every supplement checked against Guanfacine, ranked by severity Guanfacine drug information › The full plain-English guide to this medication 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 Tribulus and Guanfacine Together: Common Questions

Can you take Tribulus with Guanfacine?
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 Tribulus and Guanfacine 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

Still Have a Question About Guanfacine and Tribulus?

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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.