People of working age who are on ill health benefits sometimes get an extra amount if they've been on it for over a year. The only other common way of getting extra is if an independent (not GP) doctor decides that the persons situation has deteriorated to a severe level.
Nobody is entitled to more money because they drink/take drugs etc. If two separate doctors state someone is incapable of work and has an illness/disability, we pay them what is usually a pretty pitiful amount to lead a pretty miserable existence.
Some people claim falsely, although this figure is far lower than you probably think. There are also some who are supported by 'friendly' or incompetant doctors. Apart from that, these people are like anyone else except sick and poor. It is not a life anyone with sense would choose to live.
Does it really matter if a very small percentage of these people decide to spend some or indeed all of their benefit on alcohol? They can spend it on whatever they want and suffer the consequences. Would you complain if it all went on food or charity donations? If you had any idea how much of your taxes were wasted in far more outragous ways, maybe the nations obsession with 'that bloke down the road' would cease.