By the turn of the twenty-first century, the use of nutraceuticals became increasingly popular in both humans and animals due to their easy access, cost-effectiveness, and tolerability with a wide margin of safety. While some nutraceuticals are safe, others have a toxic potential. For a large number of nutraceuticals, no toxicity/safety data are available due to a lack of pharmacological/toxicological studies. The safety of some nutraceuticals can be compromised via contamination with toxic plants, metals, mycotoxins, pesticides, fertilizers, drugs of abuse, etc. Knowledge of pharmacokinetic/toxicokinetic studies appears to play a pivotal role in safety and toxicity assessment of nutraceuticals. Interaction studies are essential to determine efficacy, safety, and toxicity when nutraceuticals and therapeutic drugs are used concomitantly. This chapter describes various aspects of nutraceuticals, particularly their toxic potential, and the factors influencing their safety.