When a poison expires, its toxicity can change depending on the type of poison. Some poisons, like proteins, can denature or degrade over time, eventually becoming harmless. However, many other poisons are small organic molecules that can be degraded by oxidation in air, UV exposure, hydrolysis, etc. . These poisons can include nerve agents such as nicotine, sarin, and VX, which can have a lifespan of several years. Inorganic poisons, such as arsenic, only have expiration dates because they can be contaminated.

Therefore, it is not accurate to say that an expired poison is always more poisonous or less poisonous. The nature of the expired poison, which is actually in a degraded form, can vary from one substance to another. However, it is generally recommended to dispose of expired poisons properly and not to use them past their expiration date.