The 15-year-old female pug might have drunk alcohol in her bowl and breathed marijuana smoke in a confined, unventilated area of a Tamalpais Valley residence on March 25, humane society spokeswoman Carrie Harrington said.
The mother of the family that lives at the home took the dog to a veterinarian after it died, and the veterinarian called the humane society, Harrington said.
Teachers at Tamalpais High School on Monday overheard students talking about the dog's death, and a school administrator contacted the Marin County Sheriff's Office, Harrington said.
The sheriff's office also contacted the humane society, Harrington said.
The humane society is speaking to students who were at the party and is asking other witnesses to come forward, Harrington said.
A necropsy on the dog, named Coal, will be conducted outside the county, and the results should be available in a few weeks, Harrington said.
Harrington said the incident is a "great example of school administrators coming forward" so the Marin Humane Society can investigate the rumors.