An anaphrodisiac or antiaphrodisiac is something that quells or blunts the libido

Libido

Libido refers to a person's sex drive or desire for sexual activity. The desire for sex is an aspect of a person's sexuality, but varies enormously from one person to another, and it also varies depending on circumstances at a particular time. A person who has extremely frequent or a suddenly...

. It is the opposite of an aphrodisiac

Aphrodisiac

An aphrodisiac is a substance that increases sexual desire. The name comes from Aphrodite, the Greek goddess of sexuality and love. Throughout history, many foods, drinks, and behaviors have had a reputation for making sex more attainable and/or pleasurable...

, something that enhances sexual appetite. The word anaphrodisiac comes from the Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 prefix αν-, denoting negation, and the Greek goddess of love, Aphrodite

Aphrodite

Aphrodite is the Greek goddess of love, beauty, pleasure, and procreation.Her Roman equivalent is the goddess .Historically, her cult in Greece was imported from, or influenced by, the cult of Astarte in Phoenicia....

.
There are two broad sources of pharmaceutical anaphrodisiac products available for those wishing to decrease sex drive: herbal and synthetic.

Some common anaphrodisiacs are alcohol and tobacco, but this is typically an unintended consequence and not the main reason for use.