Human rights lawyer Haron Ndubi was arrested last night for drunk driving.
But Ndubi and other human rights activists say he was drugged by unknown people.
Ndubi was arrested near Gate D of State House after his car stalled on Jakaya Kikwete Road.
The lawyer was headed home when he stopped on the middle of the road and slept.
The officers tried to force him to use a breathalyser to check his alcohol concentration but he declined.
He spent the night at Kileleshwa police station and will be arraigned this morning.
Ndubi has been on the forefront in the ongoing push for electoral reforms by the opposition and civil society activists.
He is currently representing Dagoretti North MP Simba Arati in court after the state revoked the MP’s firearm licence.
The move to revoke the firearm is seen as part of the ongoing crackdown on National Resistance Movement members.
Arati is a member of the movement led by NASA boss Raila Odinga.