19d • General discussion
Tuesday Herb Study: Comfrey!
I apologize for my absence lately! I've been finishing a book, started a year long apprenticeship to get my clinical herbalist certification, preparing to launch products before the end of the year and more, so it's been taking a lot of mental space! 😅
Recently I asked myself, does harvesting comfrey after it blooms make it less potent?
After some lengthy research, the honest answer is: we need to ask, potent in what way? “Potency” can mean the level of a particular compound, the effect of a preparation, or how well it works for a particular purpose. Those are not interchangeable.
Comfrey, Symphytum officinale, has a long history as a topical herb. Its name is often linked with the idea of “knitting together,” and traditional preparations included poultices for bruises, sprains, and other injuries. Modern research has looked at topical comfrey preparations for pain and swelling. In the European Union, certain regulated comfrey root medicines are recognized for short term relief of minor sprains and bruises in adults, with use limited to 10 days. That applies to specific preparations, not every homemade comfrey remedy.
Here’s where the harvest question gets interesting! A study tracking comfrey through flower development found that pyrrolizidine alkaloids, or PAs, changed with the plant’s developmental stage. In the plants studied, PA levels rose in leaves as development progressed, while flower parts showed a particularly large increase as the flowers opened. That doesn't tell us that a post bloom harvest is less medicinally effective, though. The study measured alkaloids, not healing outcomes or a general measure of “potency.” It does suggest that timing may affect the plant’s chemical profile, including compounds we have safety concerns about.
And those PAs are the reason comfrey remains so debated in herbal circles. Some unsaturated PAs can damage the liver. Oral use of comfrey has been linked to serious liver injury, and safety authorities warn against taking comfrey internally. But, I've also heard from different cultures around the world that they sauté it and have it as a meal! PA levels also vary by plant part and preparation, so “it’s just a leaf” or “I only use a little” doesn’t establish a safe amount...unfortunately.
There is also a food history that deserves to be discussed respectfully and accurately. An ethnobotanical study from Imereti in western Georgia documents comfrey among wild greens used in regional food traditions. The authors note that prolonged cooking may reduce toxins, but also that this specific question has not been adequately studied. A documented food tradition matters, but it does not by itself tell us the PA dose, the safety of every species or preparation, or what a safe serving would be.
So where I land for now: I wouldn’t assume flowering makes comfrey less potent. I’d say the plant’s chemistry changes as it develops, and we do not have good evidence that post bloom harvesting reduces its medicinal effect. For internal use, the PA concern is serious enough that I would not recommend comfrey tea, tincture, capsules, or eating it as a safety experiment. Topical use also deserves care: use only products with clear safety information, and follow the product directions.
⭐️ Let’s talk about it: When traditional foodways and long standing herbal practice meet modern toxicology, how do you hold both respectfully?
⭐️ Have you seen research comparing comfrey chemistry before and after flowering, or have you learned a harvest rule from a teacher or tradition? Please share what you know and where you learned it.
This is an educational discussion, not a recommendation to ingest comfrey or a substitute for medical advice. 💙
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Tuesday Herb Study: Comfrey!
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