If it's true, it's not defamation. Were you busted with drugs?

The presumption of innocence applies to the finder of fact who hears your case in court. Even in court the arresting officer won't be presuming your innocence - he'll be a witness for the prosecution asserting your guilt.

Apparently he called the highway patrol because you were accusing him of harassing you. Are you describing the incident in which you were caught with drugs, or is this a different incident? What was your BAC determined to be, and were you in fact prosecuted for impaired driving? (And if so, impaired by alcohol or by drugs.)