Lehrbuch der Phytotherapie: The Textbook That Made Herbal Medicine Teachable

Before Rudolf Fritz Weiss (1895–1991), plant medicine in Germany lived mostly in two places: in the kitchens and gardens of ordinary families, and in the long memory of folk healers, monks and country doctors. It worked, people said, because it had always worked. What it lacked was a textbook a medical student could open, a set of principles a physician could test against a patient, and a way of telling a powerful plant drug from a gentle household tea. Weiss’s lifelong project was to supply exactly that. His lectures in Berlin became a book in 1944, and from 1960 that book carried the title by which a generation of German doctors knew it: the Lehrbuch der Phytotherapie, the “Textbook of Phytotherapy.”

This page follows the book and the way of thinking behind it: how wartime lectures turned into a textbook, what Weiss meant by grounding plant medicine in clinical medicine, the French physician whose “phytotherapy” he built on, his division of plant remedies into strong and mild, the difference he drew between whole natural substances and isolated pure compounds, the organ-by-organ review papers he wrote for the journal Hippokrates, the six editions he edited himself, the English translations, and the movement later called “rational phytotherapy.” His life story, the individual plants and the regulatory work of Commission E each have their own pages in this wing.

Table of Contents

  1. Lectures in Wartime Berlin
  2. From Die Pflanzenheilkunde to the Lehrbuch
  3. Observing Nature on the Ground of Clinical Medicine
  4. Henri Leclerc and the Word Phytotherapy
  5. Strong and Mild: The Forte and Mite Classification
  6. Natural Substances Versus Pure Compounds
  7. Organ by Organ: The Hippokrates Review Series
  8. Six Editions in Forty Years
  9. Herbal Medicine in English
  10. Rational Phytotherapy After Weiss
  11. Key Research Papers
  12. Connections

1. Lectures in Wartime Berlin

The textbook began as a course of lectures. From 1931, according to his German biographical record, Weiss was the lecturer (Dozent) for scientific plant medicine at the Akademie für ärztliche Fortbildung in Berlin — the Academy for Continuing Medical Education, where practising physicians came to bring their knowledge up to date. German Wikipedia’s article on plant medicine dates the founding of wissenschaftliche Pflanzenheilkunde (scientific plant medicine) in Germany to Weiss’s work from that year.

His audience was not botanists or herbalists but working doctors. That shaped everything about the material. A physician in practice needs to know which plant, in which preparation, has a recognisable effect on which kind of patient, and how that effect compares with the synthetic drugs already on the pharmacy shelf. Weiss had trained as an internist at the Charité and had studied botany alongside medicine, so he could speak both languages: the language of plant identification and the language of the hospital ward.

He kept teaching through the 1930s and into the Second World War, during which he also served as a reserve medical officer at a military hospital in Berlin-Britz (the details are on the Life and Career page). The lectures were collected and published in 1944 by the Hippokrates publishing house in Stuttgart under the title Die Pflanzenheilkunde in der ärztlichen Praxis: Vorlesungen an der Berliner Akademie für ärztliche Fortbildung — “Plant Medicine in Medical Practice: Lectures at the Berlin Academy for Continuing Medical Education.” Most sources, including Heinz Schilcher’s 1992 obituary, give 1944 as the year of the first edition; one later tribute gives 1942.

By the end of the war Weiss was a prisoner of the Soviet army, and he would not return to Germany until 1952. The book that would make his name therefore had to wait for its author before it could grow.

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2. From Die Pflanzenheilkunde to the Lehrbuch

When the second edition appeared in 1960, the title had changed. The modest German word Pflanzenheilkunde (“plant healing-lore”) gave way to the Greek-derived Phytotherapie, and the plain “lectures” became a Lehrbuch — a textbook in the full academic sense. From that edition onward the book was the Lehrbuch der Phytotherapie, published by Hippokrates in Stuttgart.

The change of name mirrored a change of ambition. A collection of lectures records what one teacher said to one audience. A textbook claims to set out a field: its principles, its methods and its body of knowledge, in an order a student can follow from the first page to the last. The aim of the book, as the physician K.-Ch. Schimmel summarised it in a 2005 tribute in the Ärztezeitschrift für Naturheilverfahren, was to lead medicinal plants out of being judged by experience alone and toward a modern therapy that could be explained by science and supported by analysis.

The years between the editions had not been idle. After his release Weiss settled as an internist in Hannover, joined the Central Association of Physicians for Naturopathy (ZÄN) in 1954 and became its first chairman in 1959. From 1956 he was publishing a steady stream of review papers on plant treatment in Hippokrates, the journal of the same publishing house (see section 7). Much of that work — the newest pharmacological findings, the clinical observations of a busy practice, the organisation of remedies by disease — flowed back into the textbook.

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3. Observing Nature on the Ground of Clinical Medicine

Weiss set out his starting point in the preface to the first edition. As Schimmel’s tribute reports it, the core of his plant medicine was knowledge that had been tested, or was at least highly probable. Its precondition was “die Kenntnis der Heilpflanzen aus der Anschauung der Natur” — knowledge of medicinal plants gained from observing nature — and for the doctor using them he always demanded “den Boden der klinischen Medizin” — the ground of clinical medicine. (The German phrases are quoted from the preface as reproduced in that tribute; the English renderings are ours.)

Two halves of one method

The two phrases describe two halves of a single method. “Observing nature” meant that a physician using plants ought to know them as living things: where they grow, which part is gathered, when it is harvested, how it smells and tastes, how it changes when dried. Weiss had written a botanical dissertation on the gypsum flora of the southern Harz mountains, and he never treated a plant drug as an anonymous powder. “The ground of clinical medicine” meant that every use of a plant had to stand up in the language of diagnosis, physiology and observed patient outcome — the same standards an internist applied to any other treatment.

Plant medicine as part of general medicine

Schimmel also notes that Weiss’s early clinical papers ranged across tuberculosis, diabetes insipidus, high blood pressure and thyroid disease, and that he always treated plant medicine as part of general medicine rather than as a rival system. This is the key to his approach. Phytotherapy, in his framing, was not an alternative to clinical medicine; it was one of its tools, to be judged by its rules. German Wikipedia sums up his achievement in one sentence: he turned phytotherapy “from an experience-based healing art into a systematic and therefore teachable and learnable science.”

Tested, or at least highly probable

The phrase “tested or at least highly probable” is also worth noticing. It is a cautious standard, not a sweeping one. It admits that much of plant medicine in the 1940s rested on long experience rather than on controlled trials, while marking a clear line between knowledge that had been checked and claims that had merely been repeated. That line would become sharper as his career went on (see section 5).

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4. Henri Leclerc and the Word Phytotherapy

Weiss did not invent the idea of a scientific plant medicine single-handed, and his admirers never claimed he did. Schimmel’s tribute places him among the pioneers who carried “die Phytotherapie LECLERCs” — the phytotherapy of Henri Leclerc — out of a purely experience-based healing art and into a scientifically graspable form, which in turn made it teachable and learnable for doctors.

Henri Leclerc (1870–1955) was a French physician who wrote on the medical use of plants in the first half of the twentieth century. The French word phytothérapie — from the Greek phyton, “plant,” and therapeia, “treatment” — is the term associated with his work. When Weiss retitled his book in 1960, he adopted that same word in its German form, Phytotherapie, rather than the older native word Pflanzenheilkunde he had used in 1944.

The choice of a Greek technical term over a homely German one carried a message. Medicine names its specialties from Greek roots — cardiology, neurology, pharmacology — and by giving plant treatment a name of the same kind, Weiss signalled that it belonged among them. The word has since become standard: Germany’s Society for Phytotherapy, which Weiss co-founded in 1971, and the Zeitschrift für Phytotherapie, which he founded as editor in 1980, both carry it.

The lineage also places Weiss in a longer European story that the site traces through other wings: from the plant catalogue of Dioscorides in the first century, through the chemical medicine of Paracelsus, to the careful clinical trial of foxglove by William Withering in the eighteenth century.

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5. Strong and Mild: The Forte and Mite Classification

One of Weiss’s best-remembered contributions is a classification. According to Schimmel’s tribute, his critical approach led him to demand that medicinal plants be divided by the strength of their action into forte and mite phytotherapeutics — Latin for “strong” and “mild.”

Why a strength scale matters

The distinction answers a problem that had muddled plant medicine for centuries. The word “herbal” covers an enormous range. At one end sit plants whose active substances act powerfully at tiny doses, where the gap between a useful amount and a dangerous one is narrow. Foxglove is the textbook example in the history of pharmacology: the glycosides it contains act directly on the heart muscle and are dosed with great precision in modern medicine, as the William Withering wing describes. At the other end sit plants used for generations as teas and household remedies, whose effects are gentle, build slowly, and leave a wide margin between a cup and an excess — chamomile flowers are a familiar example in the general pharmacological literature.

Lumping both ends together under one word causes two opposite errors: treating a strong plant drug as harmless because it is “natural,” and dismissing a mild remedy because it does not act like a strong drug. A strength scale lets a physician think about each group on its own terms — precise dosing and monitoring for the first, patience and attention to preparation for the second.

What the sources do and do not record

The sources fetched for this page record that Weiss demanded the forte/mite classification; they do not preserve a list of which plants he placed in each group. The foxglove and chamomile examples above are offered as general illustrations from the history of pharmacology, not as his own assignments.

From probability to proof

Schimmel’s tribute adds that, as his career advanced, Weiss went further and demanded proof of action and of efficacy for plant remedies. In the language of later medicine those are two different questions: does the plant do something measurable in the body (action), and does that something help patients with a given condition (efficacy)? The progression from “tested or at least highly probable” in the 1940s to an explicit demand for proof marks the direction in which he pushed the field.

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6. Natural Substances Versus Pure Compounds

The same passage in Schimmel’s tribute names a second distinction Weiss drew: between natural substances (Naturstoffe) and pure substances (Reinstoffe). The difference sounds technical, but it sits at the heart of a debate that runs through the whole history of pharmacology.

The century of the pure compound

The nineteenth century was the age of isolation. Chemists learned to extract a single active molecule from a plant and offer it in pure, weighable form. Friedrich Sertürner isolated morphine from opium in the early 1800s; the salicylates of willow bark led eventually to aspirin, as told in the Felix Hoffmann wing; the foxglove leaf gave way to purified cardiac glycosides. A pure compound has obvious advantages: its dose can be measured exactly, its effect is reproducible from batch to batch, and its mechanism can be studied in the laboratory.

The whole plant as a medicine

A natural substance in Weiss’s sense is the plant drug itself — the dried flower, leaf or root, or a tea, tincture or extract made from it. It contains not one compound but many: the main active constituents together with related substances, bitter principles, essential oils, flavonoids and more. Its strength can vary with the soil, the harvest and the preparation. Champions of plant medicine have long argued that the whole is sometimes different from its most famous part, and that some plant drugs owe their action to a mixture rather than to a single molecule.

Holding both categories

Weiss’s contribution, as the tribute records it, was to insist on keeping the two categories distinct when classifying plant medicines, rather than treating one as the true medicine and the other as a crude precursor. Read together with the forte/mite scale, the distinction gives a simple grid: a plant medicine can be strong or mild, and it can be a natural mixture or an isolated pure compound. Where a given remedy sits on that grid changes how it is prepared, how it is dosed, and what kind of evidence is needed to judge it. The individual plants he wrote about are discussed on the Hawthorn, Valerian and Chamomile page.

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7. Organ by Organ: The Hippokrates Review Series

Between the first and second editions, and for many years afterward, Weiss wrote a long run of review papers for the journal Hippokrates. PubMed indexes many of them. Most are short German-language articles without abstracts, so the list below records what each paper was about by its title, not what it concluded.

Organised by disease, not by plant

The striking feature of the series is its arrangement. Many herbals before him were organised plant by plant: here is chamomile, here is what it is good for. Weiss’s papers were organised the way a physician thinks — by disease and organ system. In 1956 he wrote on the phytotherapy of rheumatoid arthritis. In 1957 a paper numbered as part VII of his “Contributions to Phytotherapy” covered arteriosclerosis, and another the same year addressed colitis. In 1960 he wrote on medicinal plants in health care, under the heading “phyto-prevention.” In 1961 he reviewed antitussive (cough-calming) teas and other plant drugs for cough.

Single questions, examined closely

Alongside the disease reviews ran papers on single questions. In 1958 he reviewed “the present status of the Rauwolfia problem” — the Indian snakeroot whose alkaloid reserpine had recently entered medicine, a vivid modern example of a strong plant drug. In 1963 he wrote on the mechanism of action of hawthorn (Crataegus), the heart herb that would become one of German phytotherapy’s best-known remedies; it is covered further on the Hawthorn page. In 1966 he wrote in Planta Medica on bitters (Amara) in current therapy — the class of bitter-tasting plants such as gentian and wormwood used traditionally for digestion.

Keeping the reader up to date

He also wrote periodic round-ups of new findings: “Newer research results in the field of phytotherapy” in 1959 and “Results of recent phytotherapeutic research” in 1962. In 1975, at around the age of eighty, he surveyed the field as a whole in “Phytotherapy — today,” and the same year wrote on progress in treatment with medicinal plants for a dental professional journal.

Heinz Schilcher’s obituary recalls the same habit in person: at the ZÄN’s continuing-education congresses in Freudenstadt, where he lectured for half a century, “Papa Weiß” was still reporting the newest research at ninety. The review series and the textbook were two faces of one practice: gathering the latest evidence, sorting it by the diseases a doctor meets, and handing it on in teachable form.

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8. Six Editions in Forty Years

Weiss edited the book himself from the first edition of 1944 to the sixth of 1985 — a span of about forty years, most of it after the age at which other physicians retire. German Wikipedia records the sixth edition as the last he edited; Schilcher’s obituary counts a seventh edition by the time of his death in 1991, which suggests the next edition followed quickly once the book changed hands.

A book that changed with its field

Each edition had to absorb the research of its decade. Between 1944 and 1985 pharmacology itself was transformed: the antibiotic era, the arrival of modern heart, blood-pressure and psychiatric drugs, the spread of the randomised controlled trial, and a much stricter legal framework for medicines in West Germany after the 1976 Drug Law. A textbook of plant medicine written in the 1940s that had not changed would have become a historical curiosity. Weiss’s regular reviews in Hippokrates are one window into how he kept it current.

Fintelmann and the later editions

After 1985 the book passed to Volker Fintelmann, who carried it forward through further editions; later editions were continued by Fintelmann together with Kenny Kuchta. German Wikipedia lists a thirteenth edition published by Haug in 2016. Over its long life the work was translated into several languages, including Danish, English and Japanese.

The Lehrbuch was not Weiss’s only book. He also produced Das große Kneipp-Buch, linking his work to the water-cure and herbal tradition of Sebastian Kneipp; edited a continuation of Pastor Johann Künzle’s Das große Kräuterheilbuch (1974); wrote a popular guide, Moderne Pflanzen-Heilkunde (1966); and, late in life, published a book of poems. German Wikipedia credits him with more than a hundred original papers and monographs in all.

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9. Herbal Medicine in English

For most of its life the textbook was known only to readers of German. That changed in 1988 with Herbal Medicine, an English translation by A. R. Meuss (the Open Library record lists the imprint Medicina Biologica). Library catalogue records describe it as a translation of the 1985 German edition, the last Weiss edited himself, though that detail could not be confirmed from a primary record for this page.

A second English edition followed from the medical publisher Thieme in 2000, with Volker Fintelmann named as co-author, and the book has also appeared under the title Weiss’s Herbal Medicine (Thieme, 2001), later reissued as a “Classic Edition.” Catalogue descriptions describe the Thieme English text as arranged by organ system — the same disease-by-disease logic visible in his Hippokrates papers decades earlier.

The English editions mattered for a simple reason. Through the 1980s and 1990s there was a surge of interest in herbal medicine in English-speaking countries, but most of the available books were either popular herbals with little clinical grounding or highly technical works of pharmacognosy (the science of drugs of natural origin). A physician’s textbook, written by an internist for other doctors and organised around diagnoses, filled a gap. For many English-speaking readers it became their first encounter with the German tradition of phytotherapy as part of mainstream medicine.

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10. Rational Phytotherapy After Weiss

The phrase most often attached to the school that grew from his work is “rational phytotherapy.” It is worth being precise about it. The English phrase is best known as the title of a later textbook by Schulz, Hänsel and Tyler; the sources fetched for this page do not show Weiss using it of his own work. His documented terms were wissenschaftliche Pflanzenheilkunde (scientific plant medicine) and the forte/mite classification. “Rational phytotherapy” is best understood as the name later writers gave to the movement his approach made possible: plant medicine practised by physicians, judged by clinical and pharmacological evidence, and taught in medical schools.

Successors and their books

German Wikipedia names the authors who carried this line forward: Fintelmann, who continued the Lehrbuch; the pharmacist Heinz Schilcher, author of the Leitfaden Phytotherapie; and Max Wichtl, whose Teedrogen und Phytopharmaka became a standard reference on medicinal teas and plant medicines. The Zeitschrift für Phytotherapie, which Weiss founded in 1980, marked his hundred-and-twenty-fifth birthday in 2020 by reprinting a 1995 centenary editorial that called him the founder of modern phytotherapy.

The evidence debate he helped to start

His demand for proof of action and efficacy also opened a debate that continues. Once plant medicines are held to the standards of clinical medicine, some pass and some do not, and some mild remedies prove hard to test at all. In 2000 Volker Schulz argued in Phytomedicine that placebo-controlled trials can undervalue gentle remedies whose effects overlap with the psychological effects of treatment, and called for a differentiated evaluation of phytotherapy’s efficacy. That argument is his, not Weiss’s, but it grows directly from the forte/mite distinction: if strong and mild plant drugs act differently, the question of how best to measure them is a real one.

From textbook to regulation

The most concrete result of Weiss’s method came when West Germany needed to decide which old plant remedies would stay on the market under its 1976 Drug Law. The expert body that weighed the evidence, Commission E, counted Weiss among its members from its start; that story is told on the Commission E and Legacy page.

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Key Research Papers

  1. Weiss RF. [Phytotherapy of rheumatoid arthritis]. Hippokrates. 1956;27(21):685-8. PubMed PMID: 13384924
  2. Weiss RF. [Contributions to phytotherapy. VII. Phytotherapy of arteriosclerosis]. Hippokrates. 1957;28(8):247-51. PubMed PMID: 13428239
  3. Weiss RF. [Phytotherapy in colitis]. Hippokrates. 1957;28(11):348-51. PubMed PMID: 13448614
  4. Weiss RF. [The present status of the Rauwolfia problem]. Hippokrates. 1958;29(10):315-9. PubMed PMID: 13548843
  5. Weiss RF. [Newer research results in the field of phytotherapy]. Hippokrates. 1959;30(1):32-7. PubMed PMID: 13630469
  6. Weiss RF. [Medicinal plants in health care (phyto-prevention)]. Hippokrates. 1960;31:572-5. PubMed PMID: 13784094
  7. Weiss RF. [Antitussive teas and other antitussive plant drugs]. Hippokrates. 1961;32:14-8. PubMed PMID: 13784093
  8. Weiss RF. [Results of recent phytotherapeutic research]. Hippokrates. 1962;33:899-901. PubMed PMID: 13999733
  9. Weiss RF. [The mechanism of action of Crataegus oxycantha]. Hippokrates. 1963;34:602-5. PubMed PMID: 14046338
  10. Weiß R. Die Amara in der heutigen Therapie [Bitters in current therapy]. Planta Med. 1966;14(S 01):128-32. DOI: 10.1055/s-0028-1100090
  11. Weiss RF. [Phytotherapy - today]. Hippokrates. 1975;46(2):143-57. PubMed PMID: 1213908
  12. Weiss RF. [Progress in the treatment with medicinal plants]. Zahnarztl Mitt. 1975;65(14):673-4. PubMed PMID: 1060291
  13. Schulz V. The psychodynamic and pharmacodynamic effects of drugs: a differentiated evaluation of the efficacy of phytotherapy. Phytomedicine. 2000;7(1):73-81. PubMed PMID: 10782494
  14. Erinnerung an Professor R. F. Weiß – Altmeister der modernen Phytotherapie. Z Phytother. 2020;41(04):191-192. DOI: 10.1055/a-1126-9219

PubMed Topic Searches

  1. Weiss RF in Hippokrates
  2. History of phytotherapy in Germany
  3. Rational phytotherapy
  4. Evaluating the efficacy of phytotherapy

Further Reading

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Connections