Late Boneset: Benefits, Uses, and Safety Warnings

Late boneset (Eupatorium serotinum) is a perennial wildflower in the daisy family that has a long history in North American folk medicine, used primarily as a fever reducer, cold remedy, and digestive aid. Most of the formal research on boneset plants, however, has been conducted on its close relative common boneset (Eupatorium perfoliatum), and the two are often treated interchangeably in herbal traditions. While preliminary lab work hints at anti-inflammatory and immune-stimulating potential, the safety picture is complicated by the presence of pyrrolizidine alkaloids across the Eupatorium genus, compounds that can damage the liver with repeated exposure.

Late Boneset Versus Common Boneset

The Eupatorium genus contains dozens of species native to North America, and several share the “boneset” common name. Late boneset (E. serotinum) earns its name by blooming later in the season than common boneset (E. perfoliatum), typically from August through October in the eastern United States. It grows in similar habitats, favoring roadsides, field edges, and moist open ground, and produces clusters of small white flowers that look superficially like those of its more famous cousin. Common boneset is the species with the deeper ethnobotanical record and the larger body of laboratory research. When you encounter “boneset” in herbal product listings, supplement capsules, or traditional remedy books, the plant in question is almost always E. perfoliatum.

This matters because much of what people claim about late boneset’s benefits is extrapolated from studies on common boneset or from broad traditional use of the genus. The two plants share a family chemistry profile, including the pyrrolizidine alkaloids that make safety a genuine concern. A 2018 analysis that examined E. perfoliatum alongside three related Eupatorium species found that all of them contained dehydropyrrolizidine alkaloids, though concentrations varied between species and even between individual plant samples.¹ So the safety warnings that apply to common boneset apply to late boneset as well, and the claimed benefits rest on a shared but incompletely studied chemistry.

Traditional Uses and Folk Medicine Claims

Boneset plants have been fixtures in Native American and Appalachian folk medicine for centuries. Common boneset in particular was used as a tea or infusion of the whole plant for colds, sore throat, and influenza in Native American traditions, and it was credited with fever-reducing, sweat-inducing, and immune-boosting properties.² Surveys of present-day herbalists in eastern Kentucky found that locals still use boneset leaf tea as a cough suppressant and mild laxative.² The traditional list of claimed actions is long and varied:

Fever reducer: The most common historical use, sometimes specifically for the bone-deep aches of dengue-like fevers (which gave the plant its common name).
Cold and flu remedy: Whole-plant teas were drunk at the onset of upper respiratory infections to promote sweating and ease congestion.
Digestive tonic: Small doses were taken to stimulate appetite and settle the stomach, while larger doses were used as an emetic or cathartic.
Anti-inflammatory: Poultices and infusions were applied or consumed for general aches, joint pain, and inflammation.

Late boneset specifically was used in overlapping ways across the Southeast and mid-Atlantic, though it received less dedicated attention in the written herbal record than E. perfoliatum. Foragers sometimes harvested it when common boneset was past its season, treating the two as functionally similar. This substitution habit is part of why the two plants are tangled together in both folk traditions and modern herbal commerce.

What Laboratory Research Actually Shows

There are no clinical trials in humans testing late boneset for any health condition. The research that exists is almost entirely on common boneset, and it is confined to lab-bench experiments rather than studies in people. One study testing an ethanol extract of E. perfoliatum leaves found potent cytotoxicity against cultured cells, with effectiveness values comparable to chlorambucil, a standard chemotherapy drug.³ That same extract showed weak antibacterial activity against certain gram-positive bacteria, including Staphylococcus aureus.³

These findings sound dramatic, but they require careful framing. Cytotoxicity in a petri dish means the extract is good at killing cells. That is not the same as being useful against disease in a living person. Plenty of substances that destroy cells in culture are either too toxic or too poorly absorbed to work as medicines. The antibacterial effect was described as “weak,” which in practical terms means it would not compete with even a mild antibiotic. No researchers have followed up with animal studies or human trials to see whether any of these laboratory effects translate to real therapeutic benefit.

Separate lines of research on Eupatorium species have identified various classes of bioactive compounds, including flavonoids, sesquiterpene lactones, and diterpenes, that show anti-inflammatory or immunomodulatory activity in lab models. These compounds give the traditional uses some chemical plausibility. But plausibility and proof are different things, and the gap between them has not been bridged for any Eupatorium species in rigorous human trials.

Pyrrolizidine Alkaloids and the Core Safety Problem

The most important thing anyone considering late boneset should understand is the pyrrolizidine alkaloid (PA) issue. PAs are naturally occurring chemicals found in hundreds of plant species, and they are a well-documented cause of liver damage. The 2018 analysis of boneset plants found that all 49 samples of E. perfoliatum tested contained dehydropyrrolizidine alkaloids, at concentrations ranging from 0.0002% to 0.07% by weight.¹ The dominant alkaloids were lycopsamine and intermedine, along with their N-oxides and acetylated forms. Related Eupatorium species, which would include late boneset, also contained PAs.¹

A critical finding from that same study is that the way people traditionally prepare boneset concentrates the alkaloids rather than diluting them. Alcoholic tinctures and hot water infusions and decoctions were found to contain high concentrations of the alkaloids.¹ In other words, making boneset tea or tincture, the two most common folk preparations, actually pulls the toxic compounds into the liquid you drink. This is the opposite of what many herbalists assume, and it means that traditional preparation methods offer no protection against PA exposure.

The variability between plant samples (a 350-fold difference between the lowest and highest PA concentrations measured) adds another layer of unpredictability. Two batches of boneset tea brewed from plants gathered in different locations, or even from different parts of the same meadow, could deliver vastly different amounts of toxic alkaloids. You have no way to gauge your exposure without laboratory testing.

How Pyrrolizidine Alkaloids Damage the Liver

PAs themselves are not directly toxic. The problem arises after you ingest them and your liver attempts to metabolize them. Liver enzymes convert certain PAs into reactive compounds called pyrroles, which bind to proteins and DNA in liver cells and cause cumulative damage. The mechanisms include oxidative stress, triggering of programmed cell death in liver cells, and disruption of bile acid metabolism.⁴

The damage can manifest in different ways depending on the dose and duration of exposure. Acute poisoning, which is rare and typically associated with very high PA intake, can cause a condition called hepatic veno-occlusive disease, where the small veins inside the liver become blocked and the organ swells painfully. More relevant to casual herbal users is chronic low-level exposure, which can cause a slow, insidious scarring of liver tissue that may not produce symptoms for months or years. By the time someone notices the effects, significant liver damage may have already occurred.

Not all PAs are equally dangerous. The 1,2-unsaturated (dehydro) forms are the ones that get metabolized into reactive pyrroles, and these are precisely the forms found in boneset plants. Lycopsamine and intermedine, the dominant alkaloids identified in E. perfoliatum and relatives, are 1,2-unsaturated retronecine-type PAs, which means they fall squarely into the category of concern.

Allergic Reactions and the Daisy Family Connection

Beyond liver toxicity, boneset plants carry the allergy risks common to all members of the Asteraceae (daisy) family. Many Asteraceae species contain sesquiterpene lactones, which are among the most common causes of plant-related contact dermatitis. Research on Asteraceae allergy found that almost half of all sesquiterpene lactones are potential contact allergens, present in both fresh and dried plant material.⁵ The reported prevalence of allergic reactions to Asteraceae sesquiterpene lactones ranges from about 0.1% to 2.7% of the population, depending on the region studied.⁵

If you have known allergies to ragweed, chamomile, chrysanthemums, echinacea, or other daisy-family plants, you should treat boneset with extra caution. Allergic reactions can range from a skin rash where the plant touches you to more systemic reactions if you ingest a tea or tincture. Cross-reactivity within the family is common, so a ragweed allergy is a meaningful warning flag even though ragweed and boneset are different genera.

Regulatory Limits and What They Mean for You

European regulators have taken the PA risk seriously enough to set specific limits. The Herbal Medicinal Products Committee at the European Medicines Agency established a transitional daily limit of 1.0 microgram of pyrrolizidine alkaloids from any finished herbal product, a threshold that was initially set for three years and later extended.⁶ That is an extremely low limit, reflecting the seriousness of the concern. To put it in perspective, given the PA concentrations measured in boneset plants, even a single cup of boneset tea could potentially exceed that threshold many times over, depending on which plants went into the tea.

In the United States, no comparable specific limit exists for PA content in herbal products. The FDA can act against adulterated supplements after the fact but does not require pre-market PA testing. This means boneset products sold in the U.S. are not routinely tested for PA content, and the consumer has no way of knowing how much they are getting. The European regulatory approach, whatever its imperfections, at least acknowledges the problem. The American approach essentially leaves the consumer to fend for themselves.

Some herbal product manufacturers have begun voluntarily testing for PAs and marketing “PA-free” or “low-PA” boneset products, but there is no standardized verification or certification system for these claims. If you see a boneset product marketed as PA-free, you are taking the manufacturer’s word for it.

Who Should Avoid Boneset Entirely

Given the PA content and the lack of human safety data, several groups should steer clear of late boneset and common boneset alike:

People with liver disease: Any existing liver condition makes PA exposure more dangerous, since the liver is already compromised and has less capacity to handle additional toxic insults.
Pregnant or nursing women: PAs can cross the placenta and appear in breast milk. Animal studies have shown developmental toxicity from PA exposure.
Children: Lower body weight means higher relative PA exposure from the same dose, and developing livers may be more susceptible to damage.
People on medications processed by the liver: Since PAs are activated by liver enzymes, anything that changes liver enzyme activity, including common medications and alcohol, could affect how much toxic metabolite your body produces from a given PA dose.
Anyone with Asteraceae allergies: The risk of allergic reaction adds to the PA concern, making the risk-benefit ratio even less favorable.

For healthy adults who are not in any of the above categories, occasional use of boneset tea in the manner of a traditional folk remedy is probably low-risk for a single acute illness. The concern escalates sharply with repeated or daily use, because PA liver damage is cumulative. A cup of boneset tea once during a bad cold is a very different exposure profile than drinking it every day for weeks as a general tonic.

Foraging and Identification Pitfalls

Late boneset is a common wildflower across much of the eastern United States, and foragers sometimes gather it along with other Eupatorium species. Identification can be trickier than it looks. Late boneset has opposite, toothed leaves on long petioles (leaf stalks), which distinguishes it from common boneset, whose leaves appear to be pierced by the stem (a feature called “perfoliate” that gives E. perfoliatum its species name). But several other white-flowered Asteraceae species grow in the same habitats and bloom at overlapping times, including white snakeroot (Ageratina altissima), which is genuinely poisonous and has caused fatal livestock and human poisoning historically.

Confusing late boneset with white snakeroot is a real risk for inexperienced foragers. White snakeroot contains tremetol, a toxin that accumulates in the meat and milk of animals that eat it and caused “milk sickness” outbreaks in early American settlements. The two plants can grow side by side in partially shaded, moist areas, and at a glance their flower clusters look similar. If you are foraging boneset of any species, confident identification using multiple plant features, not just flower color, is essential.

The Gap Between Tradition and Evidence

Boneset occupies an awkward space in herbal medicine. The traditional use record is deep and consistent, stretching back hundreds of years across multiple cultural traditions. People clearly found it helpful for fevers and respiratory infections, and they kept using it generation after generation. That history is real and worth respecting. At the same time, the modern safety data has revealed a hazard that traditional users had no way to detect. PA-related liver damage is slow, cumulative, and often blamed on other causes. A person drinking boneset tea for winter colds who developed liver problems years later would never have connected the two.

Researchers have largely not pursued the kind of studies that could resolve this tension, such as standardized extracts with measured PA content tested in controlled human trials for cold and flu symptoms. The economics of herbal medicine research work against it: boneset is a wild plant that cannot be patented, so there is little financial incentive to fund expensive clinical trials. What exists instead is a scattering of cell-culture experiments, a solid body of phytochemical analysis, and a well-founded concern about toxicity that has not been paired with any well-founded evidence of clinical efficacy. Until that changes, anyone using late boneset or common boneset is making a decision based on tradition and plausibility rather than proven benefit, while facing a safety risk that has been measured and documented in concrete chemical terms.

1
PubMed Central. Potentially toxic pyrrolizidine alkaloids in Eupatorium perfoliatum and three related species. Implications for herbal use as boneset
2
PubMed Central. A Review and Survey of Local Eastern Kentucky Medicinal Plants and Their Pharmacological Benefits – Section: 3.5. Eupatorium perfoliatum L.
3
PubMed Central. Cytotoxicity and antibacterial activity of ethanol extract from leaves of a herbal drug, boneset (Eupatorium perfoliatum)
4
Liver Research. Pyrrolizidine alkaloids: An update on their metabolism and hepatotoxicity mechanism
5
Environmental Science and Pollution Research International. Asteraceae species as potential environmental factors of allergy
6
Food and Chemical Toxicology. Pyrrolizidine alkaloid contamination in herbal medicinal products: Limits and occurrence