Having been down the addiction route myself, let's just say I have some 'extensive' experience.
There are 2 types of addiction, a physical addiction and a psychological addiction. With a physical addiction your body goes through a physical withdrawal when the substances is stopped. Some people get the sweats, some get the shakes, some get angry, some get morose etc, etc. For some people this withdrawal can be a physical torment. In real basic terms our body's scream out for more of the substance.
With a psychological addiction, it's our minds that are screaming out for the substance. There maybe physical attributes to it, but primarily it's a mental thing. We can become psychologically addicted to anything, not just a drug. Pokie machines are a prime example of a non-drug psychological addiction.
With canna the addiction is a psychological one, not physical, unlike powders which can have a powerful physical addiction. Trying to compare a canna addiction to powders addiction is impossible as they are two different sides of the same coin and yet many try to draw a straight line between them both (usually those who have a book knowledge rather than experience). So when people make statements like "..So you'd better substitute something for marijuana..." I ask the question 'Like what? Swapping canna for a pharma opiate?' In addiction terms they call that 'Swapping the witch for the bitch'. Personally I choose the lesser of the 2 evils, canna.