Question

If any poison expires then it becomes more poisonous or less poisonous?

Answer 1

Hint: It depends on the poison. If we use the colloquial term of the word and include toxins and poisons, then many things, like proteins, will undoubtedly be denatured or degraded and eventually become harmless. For example, tetrodotoxin, ricin, botulinum, etc. I hope this poison has the shortest shelf life, because they are relatively fragile.

Complete answer:
"Not up to quality" for a poison could mean anything. It could be more toxic; it could be less. It could be differently toxic, so that it's no longer as effective against its target but could cause severe harm to other species. It only means that one chemical may have started to degrade, and the end product of that degradation could be very different.
Many other poisons are small organic molecules. These can generally be degraded by oxidation in air, UV exposure, hydrolysis, etc., and include nerve agents such as nicotine and sarin and VX. Many nerve agents have a lifespan of several years and, in fact, research has been done to extend their use in ammunition.
 Several metals are known to be toxic (such as lead, mercury, and cadmium) and are problematic because they are not only toxic in elemental form, but also inorganic and organic compounds. The toxicity of the different forms can vary greatly (see elemental mercury and methylmercury), but most forms are still at least toxic. These can last a long time because the reactions that can occur under normal conditions may not make them safe, such as a large chunk of cinnabar placed on a desk even on a geological time scale. Any significant change to make it safe.

Note:
Poison are just chemicals, and time affects them in the same way other chemicals change over time. And don't strictly stick to expiration dates, these dates are just estimated shelf life of a particular item.