Bilberry - Vaccinium myrtillus - CAUTION: Symptoms of poisoning may appear if the leaves are used over extended periods of time.

 Comfrey - Symphytum officinale - CAUTION: Comfrey contains substances called pyrroliziidine alkaloids. These are compounds that, if taken over long periods, are known to cause liver damage. Russian Comfrey contains especially high concentrations of these alkaloids and has been banned in some countries. The internal use of comfrey is a controversial subject among herbalists. This is due in part, to the fact that it's potentially carcinogenic. Due to the controversy, I would recommend avoiding this herb for internal use unless under medical supervision or the supervision of a qualified practitioner. Alternatives for Comfrey include marshmallow, peppermint, balm, and ginger.

 Horse Chestnut - Aesculus hippocastanum - CAUTION: Poisoning can occur if sufficient amounts of the leaves, seeds, or green shells are ingested. Roasting the seeds seems to destroy the poison in them.

 Hounds-Tongue - Cynoglossum officinale - CAUTION: This herb should be used with care, as it is mildly poisonous. It may also cause dermatitis in sensitive individuals.

 Marsh Tea - Ledum palustre - CAUTION: Poisoning can occur if used excessively.

 Mountain Laurel - Kalmia latifolia - CAUTION: The death of children has been recorded in instances where drinking tea from the leaves or sucking on the flowers has occurred. A toxic substance is contained in the leaves, twigs, flowers, and even the grains of pollen released from this plant.

 Pipsissewa - Chimaphila umbellata - CAUTION: This herb is generally considered safe for self administration, but it can be used for the following conditions under medical supervision; dropsy, albuminuria, hemituria, chronic kidney problems, and gonorrhea.

 Privet - Ligustrum vulgare - CAUTION: Privet berries are poisonous. Children have died from eating them.

 Rhatany - Krameria triandra - CAUTION: The root of this plant has been recommended for the following; typhoid fever and in cases where the inflammation in the alimentary system is involved. SPECIAL CARE SHOULD BE TAKEN WHEN USING FOR THESE PURPOSES.

 Rhubarb - Rheum palmatum - CAUTION: There is enough oxalic acid in the blades of the leaves to cause poisoning. The stalks do not carry this risk.

 Senna - (a) Cassia marilandica (b) Cassia acutifolia (c) Cassia angustifolia (d) Cassia fistula - CAUTION: Senna is a very powerful laxative and caution must be used in it's administration. If hemorrhoids are present or inflammation of the alimentary canal is involved, the use of this herb should be avoided.

 Sorrel - Rumex acetosa - CAUTION: Irritation of the kidneys and possibly poisoning, from mild to severe, can accompany the use of large quantities of this herb.

 Sumac - Rhus glabra - CAUTION: Many of the Sumac species are poisonous. Care should be taken to make sure proper identification is made when using this herb.

 Water Avens - Geum rivale - CAUTION: Unpleasant side effects can occur with excessive amounts of this herb.

*(Herbs in which Cautions exist. For those herbs whose Cautions are not listed on this page, a link has been provided.)