A Modern Herbal

A Modern Herbal is an herbalist book written by and first published in 1931.

It is divided into three sections: herbs and plants, poisonous herbs, and recipes. Naturally enough, the book contains much misinformation, as many (if not most) of the medical indications are bogus.

However, the toxicity assessments range from totally off to pretty accurate. (Many herbs are described both as medicines and deadly poisons, which suggests that modern-day alternative medicine's extreme avoidance of even minute amounts of potentially toxic substances is a recent innovation in herbalist thought.)

Tobacco
Tobacco is claimed to be an antiseptic and a treatment for things like asthma, parasites, and (emphasis added):

It is obvious that tobacco cannot cure any of these diseases, but the documentation of toxicity is tolerable, though no mention is made of tobacco's carcinogenicity. In recent years there has been interest in the medical establishment in nicotine as a treatment for many disorders including Alzheimer's, Parkinson's, depression, ADHD, pain, and obesity, but there is little overlap with the uses for tobacco that Grieve suggests. Also, the nicotine warning (and thus the listed side effects) are not based on traditional herbal knowledge; nicotine was not known to be a component of tobacco until scientific research on the subject was conducted in 1828. If the research had never been conducted, the entry would probably have been much more positive.

Aconite
Aconite is described as "one of our most useful drugs", capable of curing "cold, laryngitis, first stages of pneumonia and erysipelas;" and relieving "the pain of neuralgia, pleurisy and aneurism [sic]". The book describes it as being "a deadly poison", and mentions that "Aconite poisoning of wells by A. ferox has been carried out by native Indians to stop the progress of an army. They also use it for poisoning spears, darts and arrows, and for destroying tigers." Aconite is currently unproven as a treatment for any conditions.

Birthwort
Another herb listed is birthwort, which has relatively recently been found to cause cancer and kidney failure. In A Modern Herbal, no mention is made of any possible side effects:

No hint is given as to the toxicity of the herb, because, naturally, anecdotal evidence (even over hundreds of years) was not able to detect it. If herbalists had had their way, we'd have used birthwort instead of inventing the smallpox vaccine.

Lesser celandine
Lesser celandine (Ficaria verna) is said to be effective both internally and externally for piles and abscesses. Not mentioned is the fact that the herb can cause severe irritation of the gastrointestinal and urinary tracts when taken internally, and of the skin when applied topically (it may even cause blisters).

Yerba mate
Yerba maté (Ilex paraguariensis) is a "Tonic, diuretic, diaphoretic, and powerfully stimulant. In large doses it causes purging and even vomiting." No side effects are listed. But actually, yerba maté can cause cancer when taken long-term or in large doses, in addition to its caffeine-related side effects.

Germander
Germander (Teucrium spp.) is a "Stimulant, tonic, diaphoretic, diuretic," and is allegedly good for for gout, fevers, uterine obstructions, dropsy, ulcers, and snake venom poisoning. Germander may cause liver damage, cirrhosis, and hepatitis.

Comfrey
Comfrey (Symphytum spp.) is used internally as an expectorant, for "intestinal" and "lung troubles", whooping-cough, diarrhea, dysentery, and internal hemorrhage, and externally, for sprains, swellings, bruises, severe cuts, boils, abscesses, ulcers, and swelling. It is described as a "gentle remedy", and the author assures us that "In some parts of Ireland" comfrey is eaten for "defective circulation" and is "regarded as a perfectly safe and harmless remedy." In reality, internal use can cause fatal liver damage, and topical use (especially on open wounds) is discouraged, as comfrey's toxic chemicals can be absorbed through the skin. Oral comfrey products are banned in the U.K., Australia, Canada, and Germany. In rodents, orally administered comfrey is carcinogenic (for what that's worth).