Nutmeg is the seed or ground spice of several species of the genus Myristica. Myristica fragrans (fragrant nutmeg or true nutmeg) is a dark-leaved evergreen tree cultivated for two spices derived from its fruit: nutmeg, from its seed, and mace, from the seed covering. It is also a commercial source of an essential oil and nutmeg butter. The California nutmeg, Torreya californica, has a seed of similar appearance, but is not closely related to Myristica fragans, and is not used as a spice. If consumed in amounts exceeding its typical use as a spice, nutmeg powder may produce allergic reactions, cause contact dermatitis, or have psychoactive effects.

Nutmeg and mace are used for diarrhea, nausea, stomach spasms and pain, and intestinal gas. They are also used for treating cancer, kidney disease, and trouble sleeping (insomnia); increasing menstrual flow; causing a miscarriage; as a hallucinogen; and as a general tonic.

Nutmeg and mace are applied to the skin to kill pain, especially pain caused by achy joints (rheumatism), mouth sores, and toothache.

In manufacturing, nutmeg oil is used as a fragrance in soaps and cosmetics. Nutmeg oil is distilled from worm-eaten nutmeg seeds. The worms remove much of the starch and fat, leaving the portions of the seed that are rich in oil.