Butea Superba
Butea superba Roxb. / Red Kwao Krua, the Thai 'Natural PDE5' Claim
Evidence grade 2 of 5, Thin. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- Not FDA approved; sold as a dietary supplement, subject to adulteration warnings
Reference only. Not medical advice.
What can go wrong
Rat studies (Maturitas 2008) showed dose-dependent androgen disruption and cytotoxic effects at higher doses; case-level concerns about hepatic effects and cardiovascular strain exist but are poorly characterized in humans. The dominant real-world risk is undeclared PDE5-inhibitor adulteration, which can cause dangerous hypotension in men taking nitrates or with cardiovascular disease. Quality and dosing are unstandardized.
This is something to take to a clinician. The Atlas can tell you what is known about butea superba in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
Butea superba (red kwao krua) is a Thai tuberous vine rich in flavonoids and flavonoid glycosides that inhibit cyclic-AMP phosphodiesterase in vitro, the basis for its 'natural PDE5 inhibitor' marketing. Cherdshewasart's small randomized double-blind trial (2003) reported IIEF improvement in roughly 82% of men, but an open-label comparison did not beat sildenafil and the study quality is weak. Rat studies show dose-dependent androgen disruption and cytotoxicity at higher doses, and Butea products have appeared in FDA and other regulators' warnings for undeclared sildenafil/tadalafil adulteration.
Marketed as a botanical Viagra; one small trial and a rat androgen-disruption signal.
What people take it for
These are the reasons people give for taking it. They are not effects it has been shown to have.
How it is supposed to work
Isolated constituents (medicarpin, formononetin, methoxyisoflavones) inhibit cAMP phosphodiesterase in laboratory assays, which could in principle prolong smooth-muscle relaxation and support erection. The plant is also promoted as androgenic, but rat data point to androgen disruption rather than clean testosterone elevation, and no controlled human hormone data support a testosterone claim.
In-vitro PDE inhibition is not clinical efficacy
A flavonoid that inhibits PDE in a test tube is a long way from an oral drug that reliably improves erections in men. Bioavailability of these flavonoids is unquantified, the human trial base is essentially one small open study, and the plausible confounder is adulteration: products spiked with real sildenafil or tadalafil will 'work,' misattributing a pharmaceutical effect to the botanical.
What people get wrong
Often saidA natural Viagra with no downsides
ActuallyIn-vitro PDE inhibition does not equal clinical efficacy, and Butea products have a documented adulteration problem with actual PDE5 drugs.
Often saidIt raises testosterone
ActuallyHuman evidence is absent; rat data suggest androgen disruption, not clean testosterone elevation.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
Set against the alternatives
Compared with tongkat ali or horny goat weed, Butea superba has a thinner, older, and lower-quality human evidence base and a worse adulteration reputation. Any user seeking a PDE5 effect is better served by an evaluated prescription PDE5 inhibitor.
What we do not know
- Is there any placebo-controlled efficacy once adulterated products are excluded?
- What is the human hepatic and androgen-safety profile?
- Can commercial products be reliably authenticated to species and standardized?
The market for this
What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.
Wild-harvested and cultivated tubers vary widely in flavonoid content; there is no accepted standardization. Butea superba is frequently confused or co-marketed with white kwao krua (Pueraria mirifica, an estrogenic species) and with Butea monosperma, raising species-authentication concerns on top of the adulteration risk.
At a glance
- Origin
- Thailand (kwao krua daeng)
- Key actives
- Flavonoids, flavonoid glycosides (cAMP-PDE inhibition in vitro)
- Red flag
- History of PDE5-drug adulteration
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Butea Superba. A short entry is not a safe entry.
- Timeline. We have not built the dated record of research and regulatory events.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- Children and teenagers. We have not checked what is known about younger people.
- Where we land. We have not taken a position on this yet.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
Cherdshewasart & Nimsakul, Asian J Androl (RCT, double-blind)2003
IIEF improvement in ~82% of ED patients; small, short
Androgen disruption and toxicity in male rats, Maturitas2008
Dose-dependent androgen disruption and cytotoxicity
Mutagenicity assessment (BBB)2010
Extract non-mutagenic; showed antimutagenic activity in assays
Frontiers review of botanical drugs for ED2023
Notes limited, low-quality human evidence for Butea superba