To add to my previous post, I know that Valium, marijuana, and alcohol affect the dopamine system, but I also think it might be possible that the positive effects that you've noticed from having used the substances that you mentioned might be due to factors other than the effects that the substances have on dopamine or perhaps to a mixture of the effects that the substances have on dopamine and other effects that the substances have on the brain and body. I'm not sure about marijuana, but I know, for instance, that both Valium and alcohol activate the same receptors that the neurotransmitter GABA activates, so one possibility to consider is that the reason why you respond positively to Valium and alcohol might have more to due with the effects that the substances have on the GABA system than they have on the dopamine system. Of course, it might still be the case that the reason why Valium, marijuana, and alcohol have affected you in a positive way has more to do with the effects that the substances have on dopamine than with other effects that the substances might have on the brain and body, and I think it's conceivable that having a dopamine system that might be described as being underactive for one reason or another might explain why the substances that you've mentioned affect you in a positive way. But there might be other explanations, as well.