Senecionine N-oxide-D3 is a labelled analogue of Senecionine N-oxide. Senecionine N-oxide is the major pyrrolizidine alkaloid in Senecio vulgaris, a native herb of the British Isles. Senecionine N-oxide is hepatotoxic, and is suspected to be an antifertility agent in rats. Despite its toxicity, it is also being regarded as an antiproliferative agent for tumor growth.