A nightcap is a drink taken shortly before bedtime. For example, a small alcoholic drink or glass of warm milk can supposedly promote a good night's sleep.^[1][2]

Nightcaps can be neat or mixed. They should not be served chilled or on the rocks, because their point is to induce a feeling of warmth.^[3] The hot toddy is usually considered the original nightcap.^[4] Other traditional nightcaps include brown liquor like brandy or bourbon,^[3] and cream-based liqueurs such as Irish cream. Wine, especially fortified,^[5] can also function as a nightcap.^[6] Since some nightcaps are made of amaro, a digestif, they are believed to also make settling into bed easier by promoting digestion.^[4]

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 interferes with sleep quality.^[7] But, in low doses, alcohol has sleep-promoting benefits,^{[1][better source needed]} and some popular sleep medicines include 10% alcohol,^[8] although the effects of alcohol upon sleep can wear off somewhat after several nights of consecutive use.^[9]

A nightcap was originally alcoholic, since it makes the drinker feel warm and helps them sleep, just like the garment of the same name.^[10] However, warm milk is often recommended as a nightcap for inducing sleep. It contains both tryptophan and calcium.^[11] The effectiveness of warm milk for inducing sleep is disputed.^[12]

In 1930, Ovaltine was advertised as "the world's best 'night-cap' to ensure sound, natural sleep".^[10]

• Apéritif and digestif
• Sleep hygiene