Gambling is just like smoking and drinking. Immediately you become addicted, then it has become a problem. That is why is always better for one to control it early before it goes out of hand. Immediately you become addicted, you can only control it by yourself. Although it isn't easy but your self determination is the only key to help you out here.
This is true with addiction and it is always a personal decision to get out of it totally. Why I said personal decision and willingness is that some people get professional help from family but after they are off from it by third party influence, they go back to it but if they are the one that have decided to let go then they are likely to keep to their own decision. There are addicts that have not decided to let go and no matter what you do they are still glued to their addiction even slyly.
However, apart from personal decision, there are two factors that I believe can cause a gambling addict to stop and one is heavy losses and the second is life threatening outcomes like when they are warned by their doctors to stop or risk more health challenges.