Butea Superba Side Effects and Safety: What to Know

Reported Side Effects

Butea superba, also called red Kwao Krua, has a long history in Thai traditional medicine. But a long history of use is not the same as a safety record. RxList, which summarizes the Natural Medicines database, says there is not enough information to know whether Butea superba is safe or what its side effects might be. So instead of a list of “common side effects” that nobody has measured, the table below shows what researchers have actually observed, and in whom.

What Animal and Human Studies Show

In people

A randomized, double-blind, placebo-controlled trial in Thailand gave dried Butea superba tuber powder to men aged 30 to 70 with erectile dysfunction for three months. According to the PubMed abstract, the men improved on parts of a standard questionnaire, and blood counts and blood chemistry showed no apparent change. A 2023 review in Frontiers in Pharmacology adds that 39 men were enrolled, 8 dropped out, and testosterone did not change. The review also points out that the trial was small.

A second human study was an open-label trial of 32 men with erectile dysfunction, comparing a Butea superba product with sildenafil. Response rates looked similar, 84 percent for the herbal product and 81 percent for sildenafil, according to the published paper. But the story does not end there. When the men who had responded were retested in a double-blind phase using a different batch, the herbal product showed no effect. The authors concluded that the first batch had most likely been blended with a PDE5 inhibitor, which the supplier later confirmed after its own analysis. The 2023 review describes the same problem and lists headache and flushing in one man.

In short: one small randomized trial with a reassuring signal, and one study that tells us more about contamination than about the herb.

In animals

A 2008 rat study gave male rats Butea superba tuber powder by mouth for up to 90 days, at doses up to 200 mg per kg of body weight per day. Growth was not affected. At the top dose, though, white blood cell counts shifted (neutrophils down, eosinophils up) and serum creatinine fell, according to the study abstract. The Maturitas listing reports that testosterone dropped in a dose-dependent way at 150 and 200 mg per kg per day. The authors concluded that high doses had adverse effects on blood chemistry, blood counts and testosterone, and they called for awareness of the risk of overdosing.

This is animal research and cannot tell us what any dose would do in a person. It is still a good reason not to take more than a label says.

The hidden-drug problem

There is another safety issue that has nothing to do with the plant itself. The FDA has repeatedly found “natural” sexual enhancement products that secretly contain sildenafil or tadalafil. A published review of over-the-counter sexual enhancement products reports that the agency had identified more than 350 such tainted supplements, and warns that combining them with heart or blood pressure medicines can be dangerous. More recently, the FDA announced a 2025 recall of capsules sold as a male enhancement supplement after its analysis found undeclared sildenafil and tadalafil, noting that combining them with nitrates may cause a life-threatening drop in blood pressure. So, where a product comes from, and whether it is independently tested, matters as much as the plant itself.

Who Should Avoid It

These are cautions, not diagnoses. If any of them applies to you, ask your doctor or pharmacist before trying Butea superba.

• Anyone taking nitrates, for example for chest pain. The FDA warns that PDE5-inhibitor drugs can dangerously lower blood pressure with nitrates, and lab research classes Butea superba as having PDE5-inhibitory activity.
• Anyone already using sildenafil, tadalafil, vardenafil or avanafil.
• Men who take blood pressure medicine, or who have heart disease, diabetes or high cholesterol. The FDA notes that people with these conditions often take nitrates.
• Men with a hormone-related condition, or on hormone treatment, since testosterone changed at high doses in rats.
• Women who are pregnant or breastfeeding.
• Anyone who develops chest pain, fainting, sudden vision or hearing changes, or a painful erection that will not go away. Stop and get urgent medical help.

Drug Interactions

We found no formal study of Butea superba taken with other medicines. So, everything in this table is either a documented risk for a class of drug or a reasoned precaution, and the “evidence level” column says which. For the FDA’s concern about hidden drugs and nitrates, see the FDA public notification on a tainted sexual enhancement liquid.

If you are curious about how the plant may act on the PDE5 pathway in the lab, read our article on Butea superba and phosphodiesterase inhibition. For a wider look at how it compares with synthetic options, see Butea Superba vs Synthetic Enhancers, and keep in mind that no study compares their safety head to head.

Oral vs Topical Gel Safety

Many readers assume a gel must be safer because it goes on the skin. Nobody has shown that either way. We found no peer-reviewed study comparing the safety of Butea superba by mouth with a gel, and none measuring how much extract reaches the bloodstream through the skin.

What does exist is a US patent filing describing a company test in which 63 men were split into two groups and applied either a Butea superba gel or a placebo gel twice a day for one month. It also includes a skin test that the filing’s authors say showed the extract could be applied to human skin safely. A patent is a company document, not an independent peer-reviewed study, so treat it as a description of what was tested, not as proof of safety.

If you use a gel, the usual skin precautions apply. Do a patch test on a small area first, do not apply it to broken or irritated skin, wash your hands afterward, and stop if you notice redness, itching, swelling or burning. For step-by-step directions. Because we do not know how much is absorbed, the cautions in the interaction table apply to the gel too, until a doctor tells you otherwise.

Whichever form you are considering, follow the product label or ask your doctor, and never take or apply more than it says. You can read the label details on the product pages for Stherb Butea Superba Capsules and Stherb Butea Gel.

Frequently Asked Questions

What are the side effects of Butea superba?

A reference database says there is not enough information to list them. In one small trial, blood counts and blood chemistry did not change. In rats, high doses lowered testosterone and shifted white blood cell counts. A product secretly spiked with a PDE5-inhibitor drug could also cause flushing, headache and, rarely, serious problems.

Is Butea superba safe?

Its safety has not been rigorously established. It has a long history in Thai traditional use, but there are only two small human studies and no long-term data. Speak to your doctor before you try it, especially if you take regular medicines.

Is Butea superba safer than Viagra?

No research supports that statement, so we will not make it. The only study that compared the two was undermined when the herbal product was found to be probably blended with a PDE5 inhibitor. Neither should be treated as the safer choice without a doctor’s advice.

Can I take Butea superba with sildenafil or tadalafil?

Do not combine them unless your doctor agrees. Lab work classes Butea superba as having PDE5-inhibitory activity, so the effects could add up, and no study has tested the combination.

Does Butea superba affect blood pressure?

We did not find any study that measured it. Because blood pressure matters a great deal if you take nitrates or blood pressure medicine, check with your doctor or pharmacist first.

What is the right Butea superba dosage?

There is not enough scientific information to set a safe dose range. For any St.Herb product, follow the product label and never take more than the label says. The rat data is a reminder that higher doses can change blood counts and hormone levels.