The former boss of an influential Parisian think-tank and friend of French President Emmanuel Macron went on trial Thursday for allegedly spiking a colleague's glass of champagne with ecstasy.

Laurent Bigorgne, 48, stepped down as head of the Institut Montaigne in February after the colleague at the centre-right think-tank, who is also his former sister-in-law, accused him of lacing her drink before a dinner at his home.

Sophie Conrad, the younger sister of his ex-wife, told police she suspected Bigorgne planned to rape her, although the charge was not brought by prosecutors.

The bespectacled former power broker, who had taken cocaine on the night in question on February 22, faced a charge of administering harmful substances as he appeared in court on Thursday.

He risks a maximum five years in prison if convicted.

The revelations sparked shock in the close-knit political and think-tank circles of Paris where Bigorgne was known as a formidable networker and influential figure.

He was on friendly terms with Macron, providing input to his successful 2017 presidential election. His former wife lent Macron an apartment to help start his political party in 2016.

The fast-talking economist told Le Monde newspaper that after his resignation he spent time in a psychiatric hospital and underwent treatment for cocaine use.

He said he had known Conrad since she was a child and expressed regret for hurting her.

Conrad has complained that prosecutors failed to press harsher charges and has suggested Bigorgne has been treated leniently because of his connections.

"I don't know of any other motivation for putting drugs in a woman's glass other than wanting to abuse her," she told RMC radio in March.

She said she started to feel ill shortly after drinking the champagne, while a drugs test at a hospital later confirmed she had consumed MDMA, an ecstasy derivative.

The case follows a February 2021 scandal that rattled the Parisian elite after political advisor and intellectual Olivier Duhamel was accused of rape and incest.

The allegations against Duhamel, levelled in a book by writer Camille Kouchner, led to another national reckoning with sexual abuse, three years after the #MeToo movement.