One of the fundamental questions, that has already been raised here, is what do we consider addictive? Answers obviously vary, and one source one could turn to is the DSM, published by the APA. I shan’t bore you with the details of their description, but much of it is extremely functional, i.e., considers topics like social and other prices paid for the habit, inability to quit, etc.

A more physiological definition would relate to direct excitement of behavior reinforcing mechanisms. “Ah?”, you might ask. Well…
When we act in ways that have been hard-wired or soft-wired to be good for us, such as feeding and mating, we get specific responses in the brain that appear to be related to reinforcing the behavior that led to the good / pleasurable outcome. This is often, yet not always, equivalent to pleasure on a mental level. One of the major areas involved in this process is the nucleus accumbens, an area in the brain that seems to try and make sure we repeat behavior that occurred just before the secretion of a neurotransmitter named dopamine in it.

Most of the drugs we use bind to one site or more in the brain, directly or indirectly causing the secretion of said dopamine. As far as THC (the active ingredient in pot) goes, it binds both to sites in the nucleus accumbens itself, and to sites in the VTA (ventral tegemental area), indirectly causing dopamine release in the critical spot. So, if we take a physically based criteria, it seems to be addictive. Non-the-less, coffee has similar effects, and does not attract as much negative publicity.

Behavioral research hasn’t really shown any really bad effects of THC as far as I know, and only marginal health effects, so pot is probably addictive and not really healthy, but so are alcohol and nicotine and caffeine. From the four of these, marijuana probably causes more damage than coffee, and less damage than booze and cigarettes. As far as I’m concerned, people should be free to choose their own poison, as long as they don’t force it on others.