The donor tests positive for phenobarbital. The donor's dog takes phenobarbital for seizures and the donor took two of the dog's phenobarbitals to help w/sleep a few nights before the test.
I've never had, or heard, of this explanation before. Borrowed perhaps from a Seinfeld episode:
Kramer's coughs, then walks off)
JERRY: Kramer, aren't you taking any medication for that?
KRAMER: Yeah, yeah. (Pulls a bottle out of his pocket) I got some pills. They taste terrible.
JERRY: (Takes the bottle from him) Just swallow 'em.
KRAMER: (Gestures to his throat) No, my throat's too tender.
JERRY: Alright, sit down, sit down. (Grabs a pill from the bottle, and starts advancing toward Kramer - like an owner with his dog)
KRAMER: I don't want to!
(Jerry forces Kramer onto the couch. Kramer resists violently - much like a dog would)
JERRY: C'mon. Just sit down!
KRAMER: (Squirming) Jerry! What?!
JERRY: Sit down! Sit down!
KRAMER: (Struggling) Hey!
JERRY: Lean your head back. Open your mouth! (Grabs Kramer's head) Open your mouth! Open it! Open it!
(Jerry forces the pill into Kramer's mouth, then holds Kramer's mouth shut for a few moments. Thinking Kramer's already swallowed it, he lets go. Instantly, Kramer spits the pill out into the air. Jerry sighs, giving up)
JERRY: (Reads the pill bottle) What kind of pills are these, anyways?! "For Smuckers"? "May cause panting and loss of fur"? (Turns to Kramer) These are dog pills!
KRAMER: We have the same symptoms.
JERRY: But, he's a dog! You need to see a real doctor.
KRAMER: No, no. No doctors.
JERRY: Alright.. (Heads for the door, grabbing his coat)
KRAMER: Where are you going?
JERRY: I'm taking the car. I gotta run some errands. You want to go?
KRAMER: I don't know..
JERRY: (Opens the door) C'mon, you wanna go for a ride? (Starts jiggling his keys - as if he's calling out for a dog) Huh? C'mon! C'mon!
(Kramer eagerly gets up and runs out the door. Jerry follows Kramer out)