Are the tars in cannabis considerably more dangerous than those in tobacco? The claim that "the tars in cannabis are considerably more dangerous than those in tobacco" is made in Patricks An Introduction to Medicinal Chemistry (4th edition, p. 169). It's just a simple one line statement and not much attention is given to it, but from what I already knew this is to say the least a very controversial statement (see for example the independent website about drugs Erowid) and I expect better for a frequently used University level book.

The question is to what degree (from a chemical point of view) there is truth (or falsehood) to this statement given current more or less objective (not like the Heath monkey studies) knowledge? Is the author in his right to boldly state this?
This is not a complete answer (merely a step in a particular direction, namely that of the falsehood of the claim), but I contacted the author of the book (Introduction to Medicinal Chemistry) Graham Patrick and he wrote the following:


  Dear Jori,
  
  Many thanks for your e-mail and observations. Unfortunately, that
  statement was made in a very early edition of the textbook published
  over ten years ago and so I doubt if I will be able to track down the
  original reference on which it was based. As you say there is
  controversy and the statement is too sweeping. Work on the 6th edition
  is starting this year and so it will be possible to modify that
  particular passage. Many thanks for your input.
  
  Best wishes Graham