How Can I Help To Overcome Drug Addiction, Chain Smoking And Eccentric Behaviour Of My Brother ?

My brother is addicted to ganja and smokes regularly from the past 3 or more years and in the past year or two his behavior is getting eccentric, its not on a regular basis but he start acting childish some time and gets aggressive very quickly. Once a situation happened where he went out of the house at 3 in the night and returned the next afternoon and does not remember any thing, later one day when there was some issues with our neighbors and we had a fight, later in the night he went to our neighbors house to fight with then and when he discovered that he could not get into their house he start damaging other neighbors properties like breaking a car window throwing stores etc. the next day when we ask him about the scene he does not regret it nor he is sorry. This has been a serious issue any with any help is greatly appreciated.