Fifa, born in Morocco but who has represented Spain since 2015, was arrested at his home on Wednesday morning in Santa Coloma de Gramenet on the outskirts of the Catalan capital.
The 28-year-old is just one of a number of arrests being carried out in operations "for crimes against public health and the use of medications with great danger to health" said a statement from the Catalan High Court of Justice.
The Court also confirmed the operation carried out on Wednesday began with a police investigation back in June.
Fifa took advantage of Mo Farah's absence to claim European gold at the 2016 European Championships in Amsterdam.
That had been the crowning glory in an inspiring rise to fame after Fifa arrived in Spain 11 years ago as an immigrant hiding in a truck.