Green potatoes may contain a natural toxin called solanine. The greenish colour is not due to chlorophyll, but its presence indicates concentrations of solanine present in the tuber.

Solanine is a glycoalkaloid poison. It is a nerve toxin produced in the green part of the potato (the leaves, the stem, and any green spots on the skin). This bitter poisonous crystalline alkaloid is part of the plants defenses against insects, disease, and predators. Potato leaves and stems are naturally high in glycoalkaloids, so ingestion of these parts of the plant should be avoided.