Plants may often serve as sources of mild or lethal toxicity.  A few of these have been reviewed in the textbook.  These are briefly discussed below.

Pyrrolizidine Alkaloids -- May be found in ragweed (Senecio jacoboea), Heliotropium and Crotolaria spp.  They are also found in herbal preparations including borage (Borago officinalis), coltsfoot (Tussilago farfar), comfrey (Symphytum spp.), and liferoot (Senecio aureus).  They may serve as a source of food contamination (by livestock feeding on the plants, which has occurred in Australia).  A representative toxin from these plants is monocrotaline.  It forms a reactive metabolite in vivo which acutely may cause endothelial damage to the hepatic sinusoids, resulting in hæmorrhagic necrosis and ultimately causing veno-occlusion.  Chronic exposure may cause hepatic cirrhosis, which occurs in a higher incidence in the West Indies, where these plants are used as herbal teas.  Toxicity also commonly occurs in South Africa, India, and Afghanistan.
Borage -- used an an expectorant and for bronchitis, colds, inflammation, rheumatoid arthritis, and depression.

Coltsfoot -- used for asthma, bronchitis, cough

Comfrey -- used for PUD and to promote wound healing

Liferoot (Ragwort) -- used for bee stings, burns, cancerous ulcers, menstruation, and arthritis

None of the herbals have been proven effective and their potential toxicity precludes their recommendation.


Pennyroyal -- The oil from this plant is used as an over-the-counter abortifacient (it is available in health food stores as pennyroyal oil).  The volatile oils include terpinoids which may cause spontaneous abortion.  However, the dose that is required to acheive this effect will also cause renal failure.  Acute toxicity generally presents as GI upset, tachycardia, rapid shallow respirations, and potential liver failure as well.  In addition to its abortifacient actions, pennyroyal is used by herbalist as an insect repellant, and the treat chest congestion, colds, fever, flu, PMS pain, toothache, tumours, uterine fibrosis, and to increase menstruation.  It should not be recommended for any of these, since it lacks efficacy and is extremely toxic.

Ricin -- Castor beans are the source of this lectin (formerly classified as a "toxalbumin").  It is composed of two protein chains linked by disulphide bonds.  While one chain attaches to the membrane of mammalian cells, the other enters the cell.  The disulphide linkage is broken and the intracellular toxin interacts with the cellular ribosomes to inhibit protein synthesis, resulting in cell death.  One molecule of ricin will result in the death of one cell.

Bracken -- This fern contains a carcinogenic compound (ptaquiloside), that has been epidemiologically linked to an increase in throat cancer in Japan, where the fern is used as a food.  Bladder and intestinal cancers have been reported in livestock that have foraged the fern.

Borage, Coltsfoot, Comfrey, and Liferoot (See above)

Calamus (Acara calamus) -- cis-isoasoarone -- potentially carcinogenic, also hallucinogenic and produces a disulfiram-like reaction.  Also know as sweet fly or sweet root, it is used for GI problems.

Sassafras (Sassafras albidum) -- safrole -- hepatocarcinogen, hepatic inducer, causes spontaneous abortion.  As little as 5 ml of the oil may be lethal to adult and a few drops will kill a child.  It is used to treat diarrhoea and as a diaphoretic.

Chaparral (Larrea tridenta) -- nordihydroguaiaretic acid -- hepatotoxic (jaundice, greatly elevated liver enzymes, cholestasis, hepatitis, hepatocellular injury and necrosis), fatigue, pruritus.  The hepatic damage manifest 3-5 weeks following ingestion and may resolve 1-17 weeks after discontinuation.  It is used for bronchitis, colds, and skin disorders.

Germander (Teucrium chomaechrys) -- this was an adulterant in various preparation of skullcap (used an an anticonvulsant, for movement disorders, and as an anti-inflammatory).  It also causes hepatoxicity.

Licorice (Glycyrrha glabra) -- Causes pseudoaldosteronism, characterised by headache, lethargy, hypernatraemia, oedema, hypokalaemia, and hypertension progressing to congestive failure and arrest.

Ma huang (Ephedra sinica) -- ephedrine -- increases adrenergic activity causing tachycardia, hypertension, arrhythmias.  It should not be used in patients with HTN, DM, thyroid disease.

Blue Cohosh (Caulophyllum thalactroides) -- methylcytisine -- produces a nicotine-like toxicity characterised by angina, hypertension, hyperglycaemia, spontaneous abortion, and severe GI upset.  The bright blue seeds are used for rheumatism, spasms, to decrease menstruation, and to induce abortion.

Plants that irritate the oral cavity -- In most cases, the causative chemical in these plants is calcium oxalate.  Exposure (i.e. by chewing) will cause pain and œdema that may be severe enough to occlude air passages or prevent speech.  Local treatment (to the oral mucosa) most often involves the application of cold, such holding ice or ice cream in the mouth, to reduce the pain and swelling.  Ingestion of oxalate should be treated with calcium, which will chelate the oxalate and prevent its absorption.  Parenteral calcium will prevent further toxic action by absorbed oxalates.  Oxalate containing plants include Dieffenbachia (dumbcane), Sanseveria (mother-in-law's tongue), Philodendron, Caladium, and calla lilies.

Plants causing emesis without diarrhœa -- One alkaloid known to produce this effect is lycorine. These plants may cause severe, repeated vomiting that usually resolves within 24 hr.  Fluid depletion is the primary cause of concern in these patients.  Common plants containing lycorine include Narcissus spp. (Narcissus, jonquils, daffodils) and Amaryllis.

Plants producing diarrhœa with or without emesis -- Saponins are the usual causative toxins in these plants.  In addition to severe, fluid depleting diarrhœa and vomiting, they may cause respiratory depression, CNS depression, shock, and may either increase or decrease the pulse rate.  Plants that contain saponins include the deadly nightshade family (including Solanaceae such as potatoes and tomatoes -- young, green potatoes may produce mild toxicity, the plant part (not the mature tuber or fruit) may be toxic at any stage), pokeweek (Phytolacca americana, used as a food in the Southern U.S.A.), horse chesnut, blue cohosh, and English ivy (Hedera helix).

Plants that produce a delayed gastroenteritis -- signs and symptoms of toxicity may not appear for up to 48 hr after ingestion.  Plants include mistletoe (which contains a lectin similar to ricin, but less toxic), Castor (ricin, discussed above), and autumn crocus (meadow saffron, Colchicum autumnale, the source of colchicine).

Plants that cause convulsions -- The convulsions are most often due to alkaloids such as cytosine (Laburnam family) and cicutoxin (water hemlock).  Other hemlocks, including poison hemlock containing the alkaloid coniine, which has different effects, including nausea, vomiting, salivation, fever, and muscle weakness and paralysis, resulting in death by respiratory paralysis.  The specific mechanism of action of coniine is similar to curare and the depolarising neuromuscular blocking drugs.

Plants that cause anti-cholinergic-like effects -- These are well known, due to the use of the active ingredients as medicinals.  The typical effects are CNS depression, drowsiness, constipation, dry mouth, urinary retention, and tachycardia.  Plants include the atropine-containing Belladonna and hyoscyamine-containing Henbane.

Plants that cause cardiovascuar toxicity -- Similarly, several of these species are well-known by their use in medicine.  Specific plants include

Foxglove (Digitalis spp.) and oleander, that produce digoxin like effects.

Monkshood -- contains the alkaloid aconitine which will cause hypotension, reflex tachycardia, and arrhythmias (caused by opening of sodium channels).  Additionally, ingestion causes a tingling or burning of the lips, tongue, mouth, and throat.

Hellebore and other Veratrum spp. -- contain the alkaloid veratrine, which inhibits the baroreceptor response and causes hypotension.

Rhododendron -- contains grayanotoxin (andromedotoxin), exerts effects similar to veratrine.

Yew -- alkaloid taxine, produces arrhythmias that resemble those associated with hypokalæmia.  Taxine also produces nausea, vomiting, diarrhœa, abdominal pain, dyspnœa, weakness, and convulsions.

Plants that cause cyanosis -- This is generally due to cyanide toxicity, which is present in the plants.  Almond husks are high in cyanide content (the nut also contains trace amount of cyanide).  Hydrangea may also cause cyanosis.

Mushroom Toxicity -- These plants may produce a wide variety of toxic effects, dependent upon the particular species ingested.
Muscaria -- alkaloid muscarine -- cholinergic-like effects, including GI upset, sweating (NOTE that cholinergic effects are also seen with the Calabar bean, the source of the cholinesterase inhibitor physostigmine or eserine -- These two alkaloids, muscarine and eserine, act by different mechanisms to produce the same effect).

Psilocybin -- These are the hallucinogenic mushrooms, causing synæsthesia.

Coprinus -- These mushrooms will produce a disulfiram-like reaction with ethanol.

Amanita -- The "death caps", this is the most toxic mushroom family, producing severe GI upset, hepatotoxicity, nephrotoxicity, and a combination of anticholinergic and cholinergic effects, often with a latency period of up to 10 days post-ingestion.  They contain numerous toxins including phallotoxins (phalloidin, phalloin, and phallolysin) and amatoxins.

Plants that cause dermatotoxicity
These plants will cause a toxic reaction by simple exposure of the skin.  This may occur as a result of different mechanisms.
Urticaria -- Plants may cause a rash that does not involve an allergic reaction.  This is often due to histamine, acetylcholine, and serotonin that is contained in the plant.  The most common plant family to produce this effect is the nettles.

Phototoxicity -- Some plants may produce a reaction that requires exposure to sunlight to become fully manifest.  These include the plant portions of carrots, parsnips, caraway, dill, and parsley.

Topical Irritants that involve an allergic (immune-mediated) reaction -- The most common example of these plants include poison ivy, oak, and sumac (respectively Toxicodendron, formerly Rhus, radicans, diversiloba, and vernix).  The allergin in all three species is urushiol.  The urushiol is subject to limited metabolism and may persist on the skin or in blisters for quite some time.  Therefore, scratching will often spread the reaction.  Additionally, urushiol is volative and burning these plants will allow the allergin to become airbourne, from whence it may be inhaled and cause the allergic reaction within the respiratory tract.  The best treatment for the allergic reaction is systemic anti-histaminics, glucocorticoids (if severe), and local application of astringents (witch hazel, isopropanol) to help dry the rash.

Primary chemical irritants -- these plants will cause direct irritation to any surface to which they are exposed.  This may be dermatological or oral, if chewed or swallowed.  The most common species that causes this type of reaction is Euphorbia (the spurges) that include buttercups and Poinsettia.

Two Poisonous Plants of Australia

The Stinging Tree (Gimpi-Gimpi) -- This plant has thousands of silicate-based, hair-like structures on the leaves and stems.  Each of these "glass needles" contains acids and other toxins.  Exposure (which may occur by simply brushing against the plant, breaking the structure off) results in severe burning.  There is no known antidote to the toxin and exposure to cold water may cause a recurrance of the pain, as much as two months after exposure.

Cunjiboy -- This plant has been used as a treatment for the stinging tree.  The sap is applied to the area, allowed to dry, and peeled off; hopefully pulling the needles and toxin off with it.  It, however, contains oxalates, that may produce oral irritation if ingested.