<P> Traditional nightcaps include brandy, bourbon, and cream - based liqueurs such as Irish cream . Wine and beer can also function as nightcaps . </P> <P> In folk medicine, consuming a nightcap is for the purpose of inducing sleep . Alcohol is not recommended by many doctors as a sleep aid, because it may interfere with sleep quality . But, in low doses, alcohol has sleep - promoting benefits, and some popular sleep medicines include 10% alcohol, although the effects of alcohol upon sleep can wear off somewhat after several nights of consecutive use . </P> <P> Originally, a "nightcap" was understood to be alcoholic, the idea being that it warms you up and helps you sleep, just like the garment of the same name . That changed in 1930, when the non-alcoholic drink Ovaltine was advertised as "the world's best' night - cap' to ensure sound, natural sleep". An ingredient of Ovaltine is magnesium which helps to induce relaxation . </P> <P> Likewise, warm milk is often recommended as a nightcap for inducing sleep, because it contains both tryptophan and calcium . The flavor of the warm milk can be improved by adding a small amount of liqueur which may promote sleep as well; alternatively, honey and / or vanilla can improve the flavor . The effectiveness of warm milk for inducing sleep is disputed . </P>

Where does the term night cap come from
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