Yes, but I am afraid that we need to wait until he finishes the session, and if he finishes in the next hour with a big loss, I am worried that he can become mad, sad, or another negative feeling. Maybe at that time, we can let him alone and not disturb him but we need to watch out for him to make sure he does not do anything worse. That is what a real friend needs to do when he sees his friend is drops and still beside him no matter how his conditions. I am sure he will open his mind when he can calm down after losing that money.
Actually, the best option here would either take a snap of him gambling (and looking quite crazy) or let him take a peek at the amount he lost. Words aren't always enough to persuade someone, more so a person that's turned blind due to rage. It'd rather be helpful to actually present him with facts instead. I used to try talking it out with them, didn't really turn out THAT well, but it helped, albeit a little. That's why I tried turning into facts instead of encouraging words, no matter how damaging it may be.
I think we can wait for a while until they can reduce their emotions after losing some money, especially if they lose big money. If we still talk to him or suggest something to him, I bet he will not listen to us and will leave us because he will think that we can not understand him. So while he reduces the tension after playing gambling, maybe we can ask him to go to someplace, drink fresh air, and talk about something that will not relate to gambling.
After that, we can slowly talk to him and give him the facts that already happen to him. I think that can help him understand his gambling position, and we need to convince him that it is no use to stay for a long time in gambling because fact, we already lose some money.
