Joël Guerriau is being held on suspicion of drugging the woman with the intention of assaulting her, the Paris public prosecutor’s office said.
ADVERTISEMENTMP Sandrine Josso has accused the 66-year-old Senator of drugging her with ecstasy after she went to his house for dinner.
Guerriau is facing charges of "administering to a person, without their knowledge, a substance likely to impair their discernment or control over their actions in order to commit rape or sexual assault," the Paris public prosecutor's office said.
He is from the centre-right Horizons party whilst Josso, who is 48, is from the centre-right Democratic Movement party.
French station BFMTV reported on Friday that amphetamines, opiates, cannabis, cocaine, methadone and MDMA had been detected in a sample of Guerriau's blood.
Josso, who represents Loire-Atlantic for the centre-right Democratic Movement "is still in a state of shock", her lawyer, Julia Minkowski, told AFP.
"She had to deploy monumental physical and intellectual forces to overcome her terror and escape this ambush in extremis. Added to this was a feeling of betrayal and total incomprehension. Joël Guerriau had been a friend of hers for around ten years, and she trusted him completely," Minkowski added.
Rémi-Pierre Drai, the counsel for the senator, and himself an elected representative for Loire-Atlantique, said that "the confrontation enabled (his) client to forcefully confirm his version of the facts, which at this stage of the investigation does not make it possible to characterise any offence."
According to the public prosecutor, the complainant felt ill after having a drink on Tuesday night at the Paris home of the senator, with whom she did not have an intimate relationship.
According to her lawyer, Josso, "feeling faint after drinking a glass of champagne", saw Joël Guerriau "grab a small plastic bag containing something white from a drawer in his kitchen". "She then realised that he was drugging her without her knowledge", Minkowski said.
Samples taken from Ms Josso's body revealed the presence of ecstasy, the Paris public prosecutor's office said on Thursday, confirming a report by French radio station RMC. Searches were then conducted at the senator's office and at his home, where investigators found ecstasy, according to the public prosecutor's office.
"The initial evidence I have suggests that it was ecstasy," Paris public prosecutor Laure Beccuau also told RTL radio early on Friday morning.
The investigations are being conducted under the aegis of the Paris public prosecutor's office.
It has opened an investigation that doesn't need a request to be made to lift parliamentary immunity that the senator would normally have.
A banker by profession, Joël Guerriau has been an elected member of the French Senate since 2011 and is Secretary of the Senate and Vice-Chairman of the Foreign Affairs, Defence and Armed Forces Committee.