Actually the previous writeup on this is fairly wrong in alot of ways. As I understand it Dependancy can be to anything and clinical addiction is more specific.

And to be specific, addiction has 3 parts. ALL of these parts must be present, else it falls into dependancy. They are:

  1. Tolerance
  2. Reward (correct term?)
  3. Withdrawl syndrome

Tolerance means that, "the more you do it, the more you need". This is common with many drugs. People who drink alcohol may remember being drunk off one or two beers their first time drinking. Then subsequently if you keep drinking long enough, you can keep down a six pack.

Withdrawal on the other hand I can't say I know the causes of. Some withdrawal syndromes are completely psycological (and thus are not physical withdrawls - even if they feel to the user to be very phsyical - like cocaine. Cocaine has no physical cause for its withdrawl syndrome, and this is dependance forming, not addictive)

Substances are ranked on a relative scale according to each of these attributes. Those that score low on all three are not addictive. Those that score high on all of them (like nicotine and heroin which are both right at the top of all 3 catagories) are extremely addictive.

Pot ranks somewhere around where caffeine is. Somewhat less than alcohol.

Also withdrawal is not necessarily caused by excess new pain receptors, that never go away. In fact I have never heard of this as being the case. (receptors btw do get both destroyed and created though). It is more the case that the presense of the drug not only activates pleasurable receptors, it also activates the feedback mechanisms too. It can cause buildups or deficits of important chemicals in the body/brain...these take time for the body to correct. The body is used to having this other chemical level is gone.