What are medical products that undergo chemical changes or decrease in strength?

The correct choice refers to expired medicines, which are products that have a set date after which their efficacy and safety can no longer be guaranteed. Over time, medicines can undergo chemical changes that may alter their composition, potentially leading to a decrease in their potency or efficacy. This can happen due to various factors such as exposure to moisture, heat, or light. Using expired medications poses risks, as they might not provide the intended therapeutic effect and could even cause harm if the degradation products are harmful.

In contrast, other answers focus on concepts that don't relate directly to the chemical stability or therapeutic potential of medical products. Mild and serious side effects refer to adverse reactions that can occur from taking medications but do not involve the chemical integrity of the medicines themselves. Dispensing aids are tools or systems used to assist in the proper distribution of medications and are not about the changes experienced by the medicines over time. Thus, the focus on expired medicines directly relates to the issue of chemical changes and decreased strength.