As reported by the BBC:

Inhaled cannabis smoke has more harmful toxins than tobacco, scientists have discovered.

The Canadian government research found 20 times as much ammonia, a chemical linked to cancer, New Scientist said.

The Health Canada team also found five times as much hydrogen cyanide and nitrogen oxides, which are linked to heart and lung damage respectively.

But tobacco smoke contained more of a toxin linked to infertility. Experts said users must be aware of the risks.

Not sure how much truth there is, since it’s a government commissioned report, food for thought.