Pain killers are a type of medication used to reduce or eliminate pain. The two most common types of pain killers are opiates and analgesics. Opiates are a type of drug derived from the opium poppy plant and are typically used to treat moderate to severe pain. Analgesics, on the other hand, are drugs that reduce pain without causing loss of consciousness or altering a person's mental state. They are often used to treat mild to moderate pain.