Poison is any substance that is harmful to your body. Many different types of poison exist. Poisonous substances can be products you have in your house. Medicines that aren’t taken as directed can be harmful. There are several ways you can be exposed to poison. You could breathe it in, swallow it, or absorb it through your skin. Poisoning can be an accident or a planned action. The effects of poisoning depend on the substance, amount, and type of contact. Your age, weight, and state of health also affect your symptoms. Your doctor can diagnose poisoning. First, he or she will review your medical history and do a physical exam. Your doctor also can perform tests to find the cause. Most poisons can be detected in your blood or urine. Your doctor may order a toxicology screen. These checks for common drugs using a urine or saliva sample.