Probably not worth the risk. Better to use the old one as shaving cream and buy a new can for the other stuff.
It's not, once a drug hits the expiration date it should be discarded -
ReplensMD will go out of date approximately 3 years after the date of purchase. The exact expiration date is printed on the bottom of the box it comes in.
It is not recommended that you take a medication after it's expiration date. Therefore nutrofurantoin-macro will not still be effective for treating an UTI after the expiration date.
I just realized mine was a year past the expiration date, they still seem to be effective.
Maalox is no longer any good after the expiration date. When the expiration date has passed it means that it is no longer as effective as it once was.
Yeast may still be effective after its expiration date, but its potency and performance may decrease. It's best to use fresh yeast for optimal results in baking.
The contraceptive sponge is typically effective for up to 12 hours after insertion, but it can be used for multiple acts of intercourse within that time frame. The sponge itself has a shelf life of about 5 years from the date of manufacture. It's important to check the expiration date on the packaging before use, as using an expired sponge may reduce its effectiveness.
They can last forever. The only problem with using them past the expiration date is the longer the inhaler goes past the expiration date the less effective the medication will be.
Fluoride toothpaste can still be effective after its expiration date, but its potency may decrease over time. Using fluoride toothpaste past the expiration date can still help protect against tooth decay, but it may not be as effective as a product that is within its recommended shelf life.
It is best not to use any drug after its expiration date. Expiration dates are meant to reflect the stable shelf life of a medication. After this point, it may not be effective, or worse, it may contain harmful breakdown products.
The expiration date on most drugs tell you when the manufacturer is guaranteeing it will have the maximum potency. Taking a drug after the expiration date is taking a chance that it won't be as effective as a drug taken within the "guaranteed effective." So, in answer to your question, on the diphenhydramine, no one knows if it is safe. All you can say for sure, is the manufacturer will not guarantee the drug is 100% effective after the expiration date.
The expiration date is there so you know an approximate date when it should not be used. Three days before an expiration wouldn't do harm, a day or two after expiration might not do harm either, but avoid using vaccines (or any medications) that are after their expiration date.