People in some cases can become gambling addicts from poker if they don't control their usage and it gets out of control. If you're responsible and set your self limits its hard for you to become a gambling addict to online poker.

No, the truly addicted gamblers will bet on almost anything.

There is no way to stop someone from gambling unless they agree to give you money to hold. Addicts are going to find a way to gamble no matter what - even if they have to steal the money. The only thing you can do is to keep reminding your sister that you want to help her stop gambling and that you are there for moral support (but don't give her money of course!).

The precise reason that gambling can become addictive on a biological level is disputed. However, there seems to be a positive trend between gambling addiction and a particular set of genetic markers: the DRD2 gene, which is responsible for encoding the dopamine receptor d2, has been convincingly linked to gambling addiction.

Dopamine receptors are implicated in many neurological processes, including cognition, motivation and pleasure. It has been found that drugs which inhibit dopamine receptors can reduce compulsive or addictive behavior in afflicted individuals.

The up-shot of all this sciency stuff is that gambling releases chemicals that make you happy - this is what ultimately becomes addictive, not the act of gambling itself. People who describe 'gambling problems' are not necessarily addicts; a gambling problem just means gambling too much money.

A genuine addiction is a chemical and psychological pathology with particular medical characteristics. Not everyone has the capacity to easily become a gambling addict, while others will become addicted following very limited exposure.

SOURCE: http://www.rightcasino.com/news/mark-griffiths-gambling-addiction/