'Buffy the Vampire' Star Nicholas Brendon Busted in Indiana Over Prescription Drugs

According to an affidavit, obtained by TMZ, Nicholas was driving erratically when cops spotted his silver Dodge Journey last week in Vigo County, Indiana. Cops say he failed to signal and was swerving all over the place.

After he was pulled over ... cops say they noticed him sweating profusely and "appeared nervous due to a visibly racing pulse on his neck and shaking hands."

When they asked him for ID ... cops say Nicholas gave them a California ID with the name Kelton Schultz. Cops say Nicholas told them Kelton was his twin brother.

Cops claim they found a "small plastic bag that contained crystal/powder residue" and a pill bottle in a bag with a medication prescribed to "Nicholas Bender."

Cops brought out the K-9's because of "signs in the vehicle that narcotics were potentially being trafficked." One of those signs -- the new-ish car's carpeting had been cut out in multiple places and padding under the carpeting revealed evidence screws were removed.

Cops say a thorough search turned up several more plastic bags containing residue but no other contraband ... and a prescription filled that same day at a Kroger grocery store.

The prescription, cops say, was for amphetamine salts prescribed to Kelton Schultz. When asked why he lied to them about his identity, cops say Nicholas told them "they have the same prescription and they fill each other's prescription." Cops say Nicholas admitted to taking pills that were prescribed to Kelton.

They believed Nicholas was abusing the pills and or selling them and believe "he was using his brother’s ID to procure more or that the ID he initially handed me belonging to Kelton is fraudulent.” They arrested him for failure to identify and obtaining a prescription by fraud.