A 5-year-old spayed female mixed breed dog with no history of exposure to drugs or toxins presented with signs of multi-focal central nervous system (CNS) disease including ataxia, depressed mentation, and urine dribbling of two day's duration. Basic bloodwork was unremarkable, but the dog was positive for Borelia burgdorferi. The dog was hositalized for monitoring and improved dramatically within two days with only intravenous fluid administration and doxycycline. Advanced diagnostics including brain magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) analysis were within normal limits. A human urine multi-drug test performed on day 3 of hospitalization was positive for marijuana, which elicited the owner's confession that the dog had been exposed to a large amount of the drug two days prior to presentation. This paper discusses possible differentials for multi-focal CNS disease including GME and Borelia infection, the anti-inflammatory effects of doxycycline, and the accuracy of using a human urine drug test for marijuana detection in dogs. Treatment and prognosis for animals with marijuana toxicosis are also addressed.