In the 1980s the DEA in the U.S. went to court to have the scheduling changed. The judge was overruled ultimately, but he characterized cannabis as being the safest pharmaceutically active substance known.
In terms of toxicity, the toxicity is nil. There is a risk of acute discomfort that can come from too much. If you have a high dose, it can be a really unpleasant event and that could disorient you so that you might do something; you might get in an accident. In terms of harm to you, it's remarkably safe.
I would say the most substantial risk would be for people who are at risk of psychotic disorders and schizophrenia, and perhaps a psychotic bipolar. In those cases it can exacerbate symptoms and could even trigger a break, but only in people who have that predisposition, and that's a very small amount of the population.
For others I think the biggest risk is some irritation to the throat, a bronchial irritation, not long-term irritation. It's not associated with lung cancers the way tobacco is, so it's very safe.