Online Source: Medications are safe until their expiration date. After this time, they can deteriorate and do not work or can be harmful. Medicine (over-the-counter and prescribed) can become poisonous when it ages and result in death.
Always keep your medicine in its original container as this was meant to keep it safe and this will make it easier to know if medicine has expired.
I love my in-laws, but you gotta check their meds.