The L.A. County M.E.'s report also says Cameron did not have any drugs or alcohol in his system ... except for Keppra -- which is an epilepsy medication.

We broke the story ... Cameron's offical cause of death was deferred on his death certificate until the medical examiner's office could complete its investigation. The report says the 20-year-old developed non-traumatic epilepsy about 3 years ago ... and had "several major seizures" over the years.

As we told you, despite suffering epileptic seizures for a long time ... Cameron was able to achieve great acting success in both TV and in movies. The M.E.'s report says his seizures typically occurred months apart.

Boyce suffered the fatal seizure on July 6 and died in his sleep. Our sources told us his roommate found him unresponsive, and when paramedics arrived they could not revive him. He was pronounced dead at the scene.

Cameron's death led to heartfelt tributes from many celebrities, including Michelle Obama, who said, "not only did he have incredible talent, but also an incredible heart."

His family says his spirit will live on through "the kindness and compassion of all who knew and loved him." It's already evident -- the actor's favorite charity has raised thousands since his death in his honor ... with some help from his movie dad, Adam Sandler.