Supplement
Comfrey
A diclofenac-class ointment in the trials, and a liver toxin in the teapot.
Comfrey (Symphytum officinale), the folk 'knitbone,' is a plant whose root and leaves contain allantoin and rosmarinic acid (anti-inflammatory, tissue-soothing) alongside pyrrolizidine alkaloids (liver-toxic). We grade Comfrey C- on evidence and C- for worth-it at about $10-16 per month.
Evidence
Worth it
Typical cost: $10-16/month
What it does
Comfrey (Symphytum officinale), the folk 'knitbone,' is a plant whose root and leaves contain allantoin and rosmarinic acid (anti-inflammatory, tissue-soothing) alongside pyrrolizidine alkaloids (liver-toxic). It is promoted in natural-health teaching, including by Barbara O'Neill, as a poultice for injuries and, in older traditions, as a tea. Those two routes have opposite evidence and safety profiles, and this record never blends them.
What the research says
Topical comfrey root extract relieves sprain and back pain, at diclofenac's level in a head-to-head trial
Evidence: moderate. Koll 2004: the extract ointment beat placebo in acute ankle sprain (142 patients). Predel 2005: it was non-inferior to diclofenac gel in 164 sprain patients, with larger reductions in pain at rest and swelling. Giannetti 2010 (British Journal of Sports Medicine): in acute back pain, pain on movement fell dramatically more than placebo over five days. The trials were largely manufacturer-funded and tested one standardized extract (Kytta), not garden comfrey or homemade poultices.
Nothing supports taking comfrey internally, and regulators removed oral products over liver toxicity
Evidence: strong. Comfrey contains pyrrolizidine alkaloids that cause hepatic veno-occlusive disease (sinusoidal obstruction), documented in case reports including from comfrey teas, and liver tumors in rodent studies. In 2001 the FDA asked manufacturers to remove oral comfrey products from the US market; several other countries restrict or ban internal use. Traditional internal use, which persists in natural-health teaching, is the dangerous part of this plant's tradition.
The strangest profile in this grading run: an herbal topical with better trial data than most of the supplement shelf (placebo wins plus a diclofenac non-inferiority trial), attached to a plant whose internal use was removed from the market by regulators for liver toxicity. The efficacy evidence for the ointment alone would grade higher; the record grades the ingredient as promoted and sold, and its fame in natural-health teaching includes uses that can destroy a liver. C- is the average of a B-minus cream and an F-grade tea, and the safety notes do the real work on this page.
The week's longevity and biohacking news.
This grade for Comfrey rests on the record above. When a new result changes that record, the grade changes with it, and the Thursday email is where the change lands first: the week's longevity and biohacking news, in plain English, linked back to the reasoning on this page.
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Every grade follows a published rubric, and sponsors never change one. When the evidence moves a grade, Thursday is where you hear it first, before you renew a stack that stopped earning its cost.
Is it worth it?
Evidence (C-) sits below the leaderboard floor, so the worth-it grade is capped at C+ however inexpensive it is; the derived value lands at C-. About $13 a month for the standardized ointment. Derived from the October 2026 worth-it model.
Typical cost
$10-16/month
Common form, not a brand recommendation
Dosage context established
Studied topically: a standardized root extract ointment (about 10 percent extract) applied in a thin layer three to four times daily for up to 8 days for sprains and 5 days for back pain in the trials. German regulatory guidance for topical comfrey limits daily pyrrolizidine alkaloid exposure and total duration (historically no more than 4 to 6 weeks a year), on intact skin only. There is no safe established oral dose; regulators have treated internal use as unacceptable at any dose.
Worth-it leaderboard
Comfrey sits outside the worth-it top 20.
Comfrey sits outside the current top 20 on the gated leaderboard. The leaders below clear an evidence floor of B- before price counts at all, so cheap alone never earns a rank.
See the full worth-it leaderboard →
When the evidence moves a grade, this ranking moves with it. Thursday is where you hear it first.
Safety notes
Route is everything with this plant. TOPICAL: use only on intact skin, never on open wounds, broken skin, or under airtight coverings for long periods, because the toxic alkaloids absorb more readily there; keep courses short, and avoid entirely in pregnancy and breastfeeding. ORAL: do not take comfrey by mouth in any form (tea, capsules, leaves, smoothies). Its pyrrolizidine alkaloids have caused hepatic veno-occlusive disease, a sometimes fatal liver injury, and are carcinogenic in animal studies; the damage can build silently. Homemade poultices from garden comfrey are unstandardized in both directions: unknown strength and unknown alkaloid content.
Longevity Lab Report
Comfrey news. Graded when it happens.
The grade on this page stays free. The email carries the news on comfrey: expert moves, dose changes, and what is working, in plain English every Thursday.
Changelog
Last updated 2026-10-23
- 2026-10-23|Graded from the topical trial program (sprain, back pain, knee osteoarthritis) and the pyrrolizidine alkaloid toxicology record. The record separates routes absolutely: the topical extract has real evidence behind it; internal use has a real harm record behind it. Readers arriving from teaching that promotes comfrey broadly will find both halves here.
- 2026-10-23|Listed under recovery, matching this record's graded topical pain and injury evidence.