Non-toxic refers to substances that are harmless and safe for living organisms. Antonyms of non-toxic include poisonous, lethal, toxic, harmful, and dangerous. Poisonous substances can cause severe harm to living organisms, especially when ingested or inhaled. Lethal substances are capable of causing death, even in small quantities. Toxic substances can cause adverse effects on the body, including cellular damage, mutations, and cancer. Harmful substances are not inherently toxic or lethal, but they can still cause damage to the environment or living organisms. Dangerous substances can pose a risk to public health and safety, whether through explosive or flammable properties, or through a hazardous reaction with other substances.