When we live from day to day, Happiness comes in a slow drip. happiness is a chemical, it can be initiated in many ways, hard work, exercise, sex, gambling, etc, but most certainly, it is a chemical reaction in the brain..
Heroin and other opiods or opiates, completely shatters the dam, a literal tsunami of HAPPY..
Once this dam is broken, "some part" of it can recover. However, long term heroin use causes the system to so drastically change, that while plasticity is possible in the brain throughout adulthood, it does not occur at a rapid enough rate to return the person to "pre-addict" state.
Ontop of which, the Motivation-guidance system is also forever altered..
The addict, even after quitting, knows precisely how to achieve nirvana.. and it can't be overstressed, Heroin is inherently BLISS.. there's no if and or buts about it.. The abuse of which may be devastating, but principally it is the most satiate/miraculous/happiness a person can ever /feels/..
You can be a billionaire, you will never achieve the happiness level initiated by heroin..{unless you did heroin} In fact most billionaires are chasing the same brain chemical response AS heroin users through other means, but regardless, they will achieve the same level of happiness as the h-addict..
The scale of (momentary) happiness is as thus..
<slavery/poverty>-----<billionaire>-----<heroin addict>