Diphenhydramine is a generation one antihistamine, and its primary use is to prevent and counter allergies. Like many hoer antihistamines, it carries a potent hypnotic effect, and as such is often sold as a sedative as well as an allergy controlling drug. Taking more than the prescribed dose will likely not help the user to sleep better or faster, however, and in some cases this can lead to an excitatory effect - the exact opposite of what is desired. It is also worth noting that diphenhydramine builds a tolerance in the body very quickly, and after 3 days of continuous use it will present a mostly placebo effect in the user.
The other ingredient, acetaminophen, is a very widely taken world over as an analgesic, used to cope with mild pain. Whilst it is not particularly strong and doesn't lead to habit formation, it should only ever be taken in the recommended doses as the liver does not cope well with overdoses of the drug. All packaging for this medicine advises that a person seeks medical help immediately in the event of an overdose, even if the person feels well. This is because the compound can cause severe liver failure and death, and symptoms often don't set in until 24 hours after administration.
Never take more than the recommended dose of any medicine, and if you do, seek medical advice immediately.