Benefits
Traditional use as a digestive tea
The European Medicines Agency accepts boldo leaf tea and water extract as a traditional herbal medicine for indigestion (dyspepsia) and mild gut cramping, based only on long-standing use. Its assessors found no clinical trials of boldo-only products and say efficacy is only plausible, not shown. Use is limited to short courses of up to 2 weeks.
Gut transit time in healthy volunteers
In a crossover study in 12 healthy volunteers, 4 days of a dry boldo extract lengthened the time for a test sugar to reach the large bowel (about 113 vs 87 minutes with placebo). In a separate test in 43 healthy adults, a sip of bitter boldo tea did not change how quickly liquid moved through the mouth, throat or esophagus.
Bile flow in animal studies of boldine
Boldo is sold for bile flow, but this has not been measured in people. In rats, boldine, the main alkaloid, increased bile flow when infused and after 28 days of oral dosing. A hydroalcoholic boldo leaf extract did not increase bile flow in rats, so the whole-leaf effect is unconfirmed.
Liver cell responses in lab and animal studies
A hydroalcoholic boldo extract protected isolated rat liver cells and mouse livers from chemical injury in lab models, and boldine acts as an antioxidant in many lab tests. No human trial has tested liver outcomes, and published case reports link boldo tea and supplements to liver injury in people.
Mechanism of action
Boldine and bile secretion
In rats, boldine raised bile flow by an osmotic effect when infused, and 28 days of oral dosing gave a slight lasting rise in bile flow alongside more of the Bsep transporter that pumps bile acids into bile; boldine also stimulated FXR, the receptor that controls Bsep. These findings are for isolated boldine in animals; the amount reaching the liver from boldo tea in people is unknown.
Smooth muscle relaxation
In isolated rat intestine, boldine relaxed muscle contractions triggered by acetylcholine by competing at the same receptor, a possible basis for the traditional use against mild gut cramping. A 12-person human study found slower gut transit with a boldo extract, which fits but does not prove this action.
Ascaridole and why water preparations are preferred
Ascaridole is a peroxide-containing compound that makes up 16 to 38% of boldo leaf oil and is classed as highly toxic. It dissolves poorly in water, so regulators accept teas and water extracts but not powdered leaf as such or alcohol extracts. One analysis found ascaridole in all 10 commercial boldo leaf samples it tested (sold in tea bags or loose).
Clinical trials
Placebo-controlled crossover study, indexed as randomized: 2.5 g of a dry boldo extract (60% ethanol, 0.12% boldine per the EMA) or glucose placebo for 4 days each, with a lactulose hydrogen breath test on day 4. (Gotteland et al. 1995, Rev Med Chil)
12 healthy volunteers in Chile.
Oro-cecal transit time was longer with boldo than with placebo (112.5 vs 87 minutes, P < 0.05). Only transit time was measured; there were no symptom or digestion outcomes, the study was tiny and short, and the extract was an alcohol extract, a type the EU monograph does not accept for traditional herbal medicines.
Scintigraphy study comparing 5 mL of bitter boldo tea (2 g leaves boiled in 50 mL water) with 5 mL of a sweet sucrose drink, swallowed in random order. (Alves et al. 2013, Arq Gastroenterol)
43 healthy adults aged 23 to 71 without swallowing, digestive, heart or nerve problems.
No difference between the bitter boldo bolus and the sweet bolus in mouth, throat or esophageal transit, clearance or residue. The study used boldo as a bitter taste, not as a supplement dose.
Single case report of suspected herb-induced liver injury. (Piscaglia et al. 2005, Scand J Gastroenterol)
An elderly man with fatty liver who had used a herbal laxative mixture for years.
Transaminases and GGT rose several-fold within months after the maker added boldo leaf extract to the mixture; transaminases returned to normal promptly after he stopped it. One case cannot prove cause.
Single case report of suspected herb-induced liver injury. (Ribeiro et al. 2017, J Diet Suppl)
A 72-year-old woman who drank boldo leaf infusion repeatedly for 2 weeks.
She developed jaundice and raised liver enzymes; after common causes were excluded, boldo was judged the probable cause, and she recovered after stopping. The EMA notes no formal causality score was reported.
Single case report of suspected herb-induced liver injury. (Oliveira Sá et al. 2020, Eur J Case Rep Intern Med)
An 87-year-old man who had repeatedly drunk boldo leaf infusions over the previous month.
He was admitted with 2 weeks of weakness, poor appetite and jaundice. Other causes were excluded, boldo was judged the probable cause, and he recovered fully within a week of stopping. The EMA notes no formal causality score was reported.
Single case report of a suspected herb-drug interaction, with rechallenge. (Lambert et al. 2001, Pharmacotherapy)
A woman taking warfarin for atrial fibrillation who also took several natural products, including boldo and fenugreek.
Her INR rose, returned to normal a week after she stopped the products, and rose again when both were restarted. The authors rated the link to the two products together as probable; the EMA notes it cannot be concluded whether one or both contributed. The patient reported no adverse reaction.