A poison is any substance that causes injury, disease, or death through chemical means when ingested, inhaled, or otherwise absorbed into the body. Household cleaners, medicine, pesticides, gasoline, and certain plants and animals can all be poisonous. Toxins are poisons produced by living organisms (e.g., animals, plants, fungi, and bacteria), and may be used for defense or predation. Knewance Difference Engine ☺

According to the dictionary, both are the same. It's what we call synonyms.

In general usage they are interchangeable. Poison is the generic term. In biological/medical parlance toxins are poisons produced by living organisms. Hydrogen cynide is a poison but not a toxin. Venoms are poisons that are delivered through bites. Venoms may not be poisons when ingested. They become poisons when injected through the skin.