Horlicks milk was originally conceived as a powdered baby formula (via Atlas Obscura). It was made with grounded malted barley that was converted into easily digestible sugars and then added to milk. Eventually, dried milk was added to the powder to produce a high-calorie milk. Malted milk powder is now added to ice cream and milkshakes.
Because Horlicks was then marketed as a product to help people sleep, researchers in the early ’70s tested Horlicks milk to see if it worked. A 1972 study in BMJ found that hot milk mixed with Horlicks made younger people less restless during the second half of their night’s sleep. Older people slept longer and had fewer sleep disruptions. A subsequent study found that people moved less during sleep after drinking Horlicks malted milk. The researchers couldn’t explain why sleep was better after malted milk.
A 2023 review in Advances in Nutrition said that adding more carbs to milk increases the body’s ability to circulate tryptophan into the brain, which increases your serotonin and melatonin levels. Other studies have used honey and other whey protein additives to improve sleep.