Clearly, while a drug does not become ineffective after the stated expiry date, the loss of potency of a drug over time is something that drug companies are careful to notify their customers about. Just to be on the safe side. Despite the caution of drug manufacturers in this area, research shows that many drugs remain highly effective for many years after their expiry date.
For modern medicines, expiration dates are usually set for two to three years after the date of the manufacture of the drug. This is the case for veterinary liquid Nembutal which has a shelf life/ expiry date stamped on the side of the bottle. However, Exit research has shown Nembutal to be effective many years after the formal expiry date.
A further consideration in regard to drug shelf life concerns the form of the drug in question. For example is it liquid or powder as this, too, can effect its shelf life. For example, pills and capsules stored in their original, air-tight containers at cool room temperatures, free from humidity can be viable for around 10 years. This is much longer than the stated expiry date. The powdered form of a drug has similar longevity, especially if it is vacuum-packed (using a standard kitchen food vacuum-sealer)