It is not recommended to take expired Tylenol PM (acetaminophen/diphenhydramine), like any expired medication. However, there is no data to indicate that expired Tylenol PM will cause harm. It most likely will just not be as effective as an in-date product.
The recommendation not to take expired Tylenol PM includes all products in the Tylenol family, such as:
- Tylenol Extra Strength
- Tylenol 8 Hours
- Tylenol Cold and Flu
Why You Shouldn't Take Expired Tylenol PM
As stated, the reason that it not recommended to take expired Tylenol PM (and other expired medication) is that it may not be as potent as it once was when it was in-date. Most medications are less stable over time and will degrade due to a variety of factors (e.g. humidity) that accelerate decomposition. Although expired medications are more likely than non-expired medications to be less potent, it is often impossible to tell whether or not they have broken down simply by visually inspecting the medication.
You may be wondering how expiration dates are set for products like Tylenol PM. Manufacturers will perform stability tests on their product for a finite period of time, usually two to three years. After this time, there is no data to go on in regard to determining whether a medication is still as stable and potent as labeled. In other words, the expiration is marked for however long the manufacturer has stability data for.
Interestingly enough, one study, conducted in the 1980's by the FDA, found that many medications retained about 70-80% of their original potency after 10 years when stored in the original container! The issue is that there unfortunately is no definitive way to tell without testing the medication in question, which just isn't feasible or worthwhile in most cases.
Is Expired Tylenol PM Safe To Take?
Very few medications will exhibit tell-tale signs that they have gone "bad". One example in which breakdown is obvious however is aspirin. Aspirin has a characteristic vinegar smell once it begins to chemically degrade, with one of the by-products being acetic acid. Tylenol PM however, tends not to have any noticeable indicators.
It is very possible that Tylenol PM may still be good and have the expected benefit once it is expired, but again, there is no data to confirm this. Theoretically, manufacturers could perform stability tests for longer periods of time, but there generally isn't any financial incentive to do so. In addition, set expiration dates ensure that products need to be repurchased by a retailer/wholesaler once existing products expire. The good news is that there are no reports of expired Tylenol PM products causing harm to anyone as Tylenol PM doesn't break down into harmful components.
The main concern is that expired Tylenol PM simply may not work as well as in-date products. As Tylenol PM is available over the counter and is relatively inexpensive, it makes sense to buy a new, replacement product to ensure potency.