If you've ever noticed an expiration date on the back of your box of paracetamol, you've probably wondered about its ridiculously short shelf-life. “Expires after two years? Pfft, but what harm could they really do?”.
In 1979, the Food and Drug Administration (FDA) commissioned the addition of expiration dates to all medicines in the US, from prescription and over-the-counter drugs, to herbal supplements. However, their definition of “expiration” may not be as sinister as you might expect: after the calculated expiration date, the manufacturer can no longer guarantee the original potency - but this isn't to say that they're dangerous or no longer effective after this date.
As it stands, studies have proven that expiration dates may not always be as important as they're cracked up to be. Studies by the FDA showed that a collection of drugs from a military stockpile were still viable even 15 years beyond the expiration date, and that with proper storage their shelf-life could be extended further still. These findings were supported by a study published in the Journal Archives of Internal Medicine, which showed that eight simple drugs (containing only a few active ingredients) still contained 90% of their active ingredients 28-40 years after the expiration date, therefore remaining viable.
However, it was also found that the active ingredients aspirin and amphetamine were present in amounts of less than 90%, indicating that drugs containing these compounds would not be as effective past their use-by dates. So it seems that it really depends on the type of medicine. While some simple drugs may be safe to take and could still go some way towards alleviating your symptoms, others may be less effective after all.
An example of a medicine with a proven short shelf-life, and which should definitely be replaced after its expiration date is the Epipen. The active ingredient epinephrine is unstable and oxidises (breaks down) with exposure to light, air and high temperatures, leading its expiration only one year after manufacture. Given its role in treating potentially life-threatening anaphylactic shocks, it is essential that they're replaced once they have expired. Although, it has been suggested that outdated Epipens could be used in absolute emergencies, as long as there is no discolouration or precipitate present. Other similarly unstable medicines include insulin and nitroglycerin.
Liquid antibiotics (mixtures of water and powdered antibiotic) should also be avoided beyond the expiry date assigned by your pharmacist (1-2 weeks after preparation). Mixing the antibiotic with water decreases its original stability, therefore shortening the length of time that it remains at full potency. Using an antibiotic with decreased potency provides multiple issues, firstly in being unable to treat your infection as effectively and efficiently, and secondly in its potential contribution to antibiotic resistance.
Despite studies proving that some medicines can last for decades, and a lack of any conclusive report on any toxic effects in consumption of expired medicines, the FDA currently advises to not use any medicines beyond their use-by date. FDA pharmacist Ilisa Bernstein is quoted as saying very directly “If your medicine has expired, do not use it.”, just to be on the safe side. It's easy to see where they're coming from, but this conservative approach could ironically be costing the medical industry billions of dollars in the wastage of unused, perfectly viable medicines.
So if you find yourself with that expired paracetamol and can't be bothered to go to the shops for a new packet, use your own judgement, it's not guaranteed to be 100% effective but as long as it's been stored in a dry, cool space then it could still have some worth.
Just be careful with essential medicines like the Epipen and insulin, while it may seem like a great conspiracy by drug manufacturers to just get as much money out of us as possible, make sure to abide by the use-by dates and replace the medicines when needed. If you're in any doubt about whether a specific medicine can be used beyond it's expiration date, ask your GP or pharmacist.