The expiry date of medicinal products is not the mere consequence of arbitrary considerations or commercial logic, but derives from scientific evidence. It is in fact the result of an evaluation based on stability studies conducted on drugs. The methods used to carry out these tests are standardized and regulated by protocols reported in the ICH international guidelines which are followed in Europe, the United States and Japan.
The stability studies conducted by pharmaceutical companies are reported in specific sections of the dossier that accompanies the registration of a drug and which is submitted to AIFA for the granting of the Marketing Authorisation. The 
period of validity of a medicinal product (which leads to the definition of the expiry date) is therefore authorized on the basis of the evaluation carried out by the Agency's experts on the values (precise numbers and parameters) deriving from the studies. The same goes for the authorized conservation conditions, which are only those for which there are supporting elements.
It is not advisable for the patient to evaluate whether an expired drug is usable or not and what its danger is by autonomously considering the colour, the smell or the changes in consistency. In fact, over time there may be a degradation of the active principle which in addition to affecting its effectiveness, can lead to risks in terms of safety. The degradation of active principle or of the excipients contained in the medicinal product could put the patient's life at serious risk, for example due to a fatal allergic reaction, even at very low doses, caused by the impurities. It is worth remembering that the expiry date refers to the medicine stored in its intact container and in standard temperature and humidity conditions, so a medicine stored for years at home, perhaps incorrectly, will degrade faster .
Proper storage of medicines serves to keep their pharmacological and therapeutic characteristics unaltered for the entire period of validity indicated on the packaging, as it guarantees their stability, an essential requirement for them to fully perform the expected therapeutic activity. It is best to keep medicines in a cool, dry place in the house (not in the bathroom), away from heat sources, in the original labeled containers. Often the negative effects of light, air and sudden changes in temperature, due to the repeated opening of the package, can deteriorate the active principle; in these cases it is good practice to note the date of first opening on the package. It is always of fundamental importance to follow the information on storage given in the package leaflet of each medicine.
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