Adrenaline is not the only thing what is causing you too be hooked on a gambling activities.
It is pleasure to feel rush an increased number of hormones in your head but mechanism is far more complicated.
It is a mixture of pleasure, anticipation, greed and lack of something in life that make you an addict.
Anticipation, curiosity and surprize is probably the biggest factor.
If there is a stable investment that you know will earn you 1% you wont get excited about it, because you know the outcome.
But if you bet 15,000$ in a 10% wirate scenario with the anticipation of winning 100,000$, or losing 15,000$, then its the surprize that keeps you going.
You cannot know if you end up big winner or big loser. And
curiosity is one of the driving forces of humans!