I'm not so sure if we can actually draw lines between physical and psychological since brain can control your needs and wants. People can get addicted to anything and withdrawals suck.
There are some things are genuinely physical. Here is an example: Marijuana is known to constrict the vessels of the brain. Over the long term, the brain compensates for this to return the vessels to a normal state. When you suddenly stop smoking cannabis routinely, the vessels expand because the THC is not maintaining their restriction. Expanded vessels in the brain are a common suspected cause of migraines, and severe headaches are a top reported symptom of cannabis withdrawal. Interestingly, this effect of cannabis on the brain's vascular system also makes it a highly-researched drug for migraine treatment. It would be like taking migraine medication every day for a long time, then suddenly stopping and getting a flood of headaches as the brain re-adjusts.
