Abstract The chemical analysis of Conium maculatum revealed that the plant contained alkaloids, flavonoids, coumarins, polyacetylenes, vitamins, oils and many other active metabolites. The alkaloidal fraction of Conium maculatum aerial parts exhibited significant anti-inflammatory activity in rats and strong peripheral and central antinociceptive effects in mice with a narrow dose range (10–20 mg/kg). It was found to be lethal in doses higher than 20 mg/kg. However, hemlock (Conium maculatum) was one of the most poisonous plants for laboratory animals, farm animal and human being, due to the presence of piperidine alkaloids in all parts of the plant, including the leaves, flowers, fruits, seeds, and roots. In the current work, the chemical constituents, pharmacological and toxicological effects of Conium maculatum were reviewed.