Tonic may refer to:

• Tonic water, a drink traditionally containing quinine
• Regional name for soft drink—a carbonated beverage, used in eastern Massachusetts and parts of Maine and New Hampshire.
• Tonic (physiology), the response of a muscle fiber or nerve ending typified by slow, continuous action
• Tonic syllable, the stressed syllable of a word
• Herbal tonic, a herbal medicine with tonic effects
• Tonic (music), the tonal center of a musical scale
• Tonic (band), an American rock band
• Tonic , 2010
• Tonic, a New York City music venue, 1998–2007
• Tonic , 2000
• Tonic , Canadian radio program
• Tonic suit, a garment made from a shiny mohair blend that was fashionable among the Mods of the mid 1960s
• Tonic (film), a Bengali film