According to some medical experts and governmental bodies including the Food and Drug Administration (FDA), you should never use expired medications. Instead, you should dispose of them properly. 
However, this has raised controversy with opponents saying that such medicines are not necessarily harmful and can still be used depending on when they actually expired. Here are some of the safety issues surrounding expired medicine.
Expiration Date
The Food and Drug Administration (FDA) requires all drug manufacturers to put expiration dates on their products–both prescription and over-the-counter drugs. Consequently, drug manufacturers usually print the expiration date along with the date of the manufacture/production on a label attached to the medicine package/bottle, or stamp the date on the bottom or the cap of a medicine bottle. In essence, the expiration date simply refers to the date until which the manufacturer can guarantee 100% potency and safety of the medicine. This means medicines that have already expired may be harmful to human health or may not be potent enough to work as expected. To encourage people of dispose of expired medicines, pharmacists typically put “discard after” or “beyond use” labels on medications dispensed to patients. In fact, 17 states in the US have enacted laws that require pharmacists to put such labels on drugs. This expiration or “discard after” date normally falls anywhere between 12 and 60 months of the manufacturing date, according to Dr. Sharon Bergquist, assistant professor of medicine at Amory University in Atlanta.
Efficacy of Expired Medicine
Expired medications tend to lose their potency over time. In fact, research published in The Medical Letter on Drugs and Therapeutics says that most medications retain approximately 70 to 80% of their original potency for up to two years after their expiration dates. Surprisingly, this is true for some drugs in containers/packages/bottles that have been opened. However, this does not apply to prescription medicines including insulin, liquid antibiotics and nitroglycerin, according to the Institute for Safe Medication Practices (ISMP). Another clinical study commissioned by the Department of Defense found that 88% of 122 drugs analyzed remained fully potent anywhere from 6 months to 5½ years after their expiration dates. In fact, some of these medicines were fully potent and safe to use for up to 15 years after their expiration dates. Nevertheless, the researchers involved in this study noted that the drugs were kept in a climate-controlled environment, which extended their shelf lives. Drugs in solid form such as capsules and tablets maintain their potency well after their expiration dates much better than drugs in suspension or solution form, whereas drugs that require refrigeration tend to lose their potency the fastest. This is according to the FDA.
Using Expired Medicine
According to Dr. Bergquist, patients taking medications for life-threatening medical conditions should avoid expired medicine because such medication could cause toxicity among other health complications. On the other hand, Dr. Bergquist says you can take an expired pain or headache drug if it is all you have and cannot access other medicines at the time.
Risks of Using Expired Drugs
Firstly, the US Drug Enforcement Administration (DEA) says that certain prescription medicines, such as painkillers, are prone to diversion and misuse/abuse even after they have expired. Secondly, expired antibiotics could fail to treat infections or even cause a person to develop resistance to antibiotics. Finally, children or pets could accidentally ingest expired medications leading to serious health complications.
When to Discard Drugs
To start with, it is advisable to dispose of any medication that is well past its expiration date. Additionally, you should discard any drug in solution or suspension form if it appears cloudy, discolored, or forms a precipitant even if its expiry date has not elapsed. If you carry an EpiPen autoinjector, discard it after the expiration date because epinephrine loses its potency thereafter. The American Association of Poison Control Centers (AAPCC) recommends taking all expired medications to a pharmacy, hospital, or community-based take-back program for proper disposal.
Conclusion
Although some medicines remain highly potent and safe to use long past their expiration dates, you should not use such medicines because they might be unsafe. What’s more, you should pay special attention to the expiration dates on medicines that require refrigeration, as well as medicines that must be reconstituted in suspension form.
This is controversial, and personally, I am ambivalent, so feel free to comment.