Over the last two years, various liquids have been thrown at iconic paintings in the gallery on Trafalgar Square, including Vincent van Gogh's "Sunflowers" and John Constable's "The Hay Wain".
From Friday, the gallery said all liquids would be banned, except baby formula, expressed breast milk and prescription medicines.
The attacks "have caused physical damage to the artworks, distress to visitors and staff alike, and disruption to our mission to ensure great art is available for everyone, everywhere to enjoy," it said.
Theatrical attacks on paintings and sit-in protests at the National Gallery have been a way for activists to protest the climate crisis and other causes, arguing that art is "worthless" if the climate and human life are threatened.
Last week, two people were arrested after pasting a photo of a bloodied mother and child in Gaza over a Picasso painting, calling for an arms embargo on Israel.
Van Gogh's "Sunflowers" has been the target of two attacks.
Three people from the Just Stop Oil group threw soup at the painting in September, after two other JSO activists were jailed for committing a similar act in 2022.
The pair who targeted "Sunflowers" two years ago were sentenced to 20 months and two years in prison.
Just Stop Oil and Youth Demand on Wednesday wrote an open letter to the National Museum Directors' Council, offering to meet them at the Gallery for talks.
It said its protests were part of a proud tradition dating back to the Suffragette movement, and its actions "cause small amounts of damage and disruption" to highlight global warming and the dangers of fossil fuels.
"The arts are unsuccessful in refuting climate denial. Politics has failed us. Resistance is our only remaining option," the groups said.
