Decaux had been due to compete in the world championships, which begin in Moscow on Saturday, but did not travel with the French team following her hearing on Thursday.
"She took a supplement containing amphetamines at the European team championships in Gateshead, England in June,"
Michel Marle, head of French federation disciplinary committee told Reuters.
"She is provisionally suspended and cannot take part in the world championships."
Decaux finished fourth in the Gateshead 100m hurdles in 12.94 seconds but recorded a personal best 12.7 seconds in the French championships on July 13 to promote herself into a potential finalist at the world championships.
The 28-year-old now faces a two-year ban.