I think it is bigger addiction than that of drugs because it can happen that the drugs supply discontinues due to some reasons but these gambling casinos will never be stopped or banned in the country where gambling has more followers because these casinos are paying huge amount of taxes to the governments as well as other amounts.
I would not say it is bigger addiction than drugs since most of the time; the both of them actually play in the same way since they are the kind of addiction that renders their victim irresponsibly useless anyway.
Most psychologists believe that it is the same part of the brain affected by drug addiction that gambling addiction also tends to affect which is more like playing with the mind until it ruins. People's mindset towards gambling is what sets in the addiction, and looking at the fact that the possibility of losing is huge, I still wonder why a lot of people take such risk when there could be better risks to take.