Poisonous plants are divided into several groups according to the chemicals they contain. The most dangerous contain one of these three chemicals — solanine, grayanotoxins, and cardiac glycosides.

Solanine is found in food and ornamental plants. Unripe tomatoes and the green "eyes" of potatoes contain solanine that can cause moderate nausea, vomiting, headache and diarrhea. Eating large quantities can cause drowsiness, sweating, as well as changes in blood pressure and heart rate. Most effects are seen within two to 24 hours. Diarrhea may last for three to six days.

The major effects of eating plants containing grayanotoxins are immediate. Eating or chewing on leaves of this plant group — including azaleas and rhododendrons — can cause burning, numbness and tingling of the mouth. Two to three hours later, other signs of poisoning may occur, including nausea, vomiting, sweating, confusion, and slowing of the heart rate. There have been reports of seizures with severe overdoses. Azalea leaves are particularly dangerous; swallowing three or more leaves is cause for concern. Grayanotoxins are also present in Lambkill and Mountain Laurel.

Plants that contain cardiac glycoside can cause changes in the rate or rhythm of the heart. Many heart medications currently on the market are derived from these plants. Poisoning with cardiac glycosides often occurs when these plants are incorrectly used as a tea. The initial signs of poisoning are headache, confusion, dizziness, vomiting, or stomach pain. Later, effects on heart rate and blood pressure occur. Glycosides are found in Foxglove, Lily-of-the-Valley, Oleander and Squill. (Not an all-inclusive list.)

Many toxic plants produce very minor symptoms such as a stomach upset, mouth and throat pain or skin rash. If large quantities are swallowed, or if a person frequently takes smaller amounts of the plant, more serious symptoms could develop. Although some people are more sensitive to the toxic effects of plants than others, monitor small children at al times when in the presence of plants.