• Tonic (music), a concept of musical theory
• Tonic (band), an American post-grunge rock band
• Tonic (music club), a New York City music venue, 1998-2007
• Tonic (album), a 2000 album by Medeski Martin & Wood
• Tonic (physiology), a muscle which is predominantly toned
• Tonic water, a carbonated beverage flavored with quinine
• Tonic, regional name for a soft drink, common in New England
• Tonic (radio program), a radio program on CBC 2

Tonic may also be:

• A usually liquid drug given to improve health
• A patent medicine that claims to have tonic properties