Sam Lutfi -- I NEVER Gave Britney Spears Adderall

Britney Spears' former manager just took the stand in his defamation case against the singer's family ... insisting he NEVER enabled Brit with Adderall ... despite allegations to the contrary.

Sam Lutfi testified in open court moments ago .. that he has an Rx for Adderall because of his ADD -- he takes two doses a day -- but he's adamant ... he never shared his meds with Britney ... or anyone else.

Britney's mother Lynne had accused Sam of fueling the singer with drugs, but Sam says that's just not true.

Britney's parents Jamie and Lynne Spears were photographed arriving to court this afternoon looking battle-ready.