It is not generally considered to, however I recently read a study that indicated that long term opiate abuse may cause damage to the temporal lobes, possibly resulting in epilepsy. This is probably...
Yes. It causes CNS depression much like alcohol does - and is addictive when taken for long periods of time. Usually greater than 2 weeks.
Can? It might be possible but it's unlikely. Back problems are related to lifting.
heart attack or stroke
Yes any long term pain medication can cause liver damage.