I have used morphine for chronic pain since 2006.  I use it concurrently with an oil extractive of marijuana, this almost completely negates the rebound back pain often associated with opiates.  I was told it was the marijuana the prevented a tolerance build up as well.
This was incorrect, I am one of the ten percent that can take opiates with out craving more or building a tolerance.  I take the same 7.5 mg daily now as I did in 2006 and receive the same effect.
There is another ten percent of the population that becomes addicted almost immediately.  In the small group counselling sessions it became obvious two members were addicted, one died from opiate complications, the other was hospitalized until the withdrawal was no longer life threatening.
Taking out those two addicts and my intolerance the balance of the pain clinic members had varying degrees of success.  Dosages went up, some faster, some slower, but other than myself all had dosage increases.  Other than the two addicted members the increases in dosage remained within the safe range.  The third that used marijuana had fewer problems than the two thirds that did not.
A single blanket law is not going to change the biological effects on humans.  Politicians need to butt out and let the doctors handle this on individual patient needs.