Cave murals found in Spain appear to depict them in religious rituals - which would be the oldest evidence of their use in Europe.
The Selva Pascuala cave mural near the town of Villar del Humo has a bull in the centre, but researchers from America and Mexico are focussing on a row of 13 small mushroom-like objects.
Brian Akers at Pasco-Hernando Community College in Florida, and Gaston Guzman at the Ecological Institute of Xalapa in Mexico say they believe the objects are Psilocybe hispanica, a local funghi with hallucinogenic properties.
The mushroom has a bell-shaped cap with a dome and lacks a ring around the stalk, just like the objects in the 6,000 year-old mural, they say.
It also has stalks which vary from straight to sinuous - the same as those drawn thousands of years ago, they add in the latest issue of New Scientist.
But, even though it is several millennia old, it is not thought to be the oldest painting showing hallucinogenic mushrooms.
A mural in Algeria that may show Psilocybe mairei is 7,000 to 9,000 years old, according to NewScientist.com.