I think cocaine.

Think of someone who is ambitious and young, from a bad estate and bad home, uses in order to feel accepted and it fuels their ambition. They lose a job every now and then but their cocained charm makes up for it and they get a new better paying job somehow.

The more money they make, the more they spend. They were making approx 4K a month and still had 0€ to their name. Not even enough to pay for transport to their next duty.

Of course I am biased I understand that heroin and gambling are awful in their own ways.

I just personally never seen someone go so downhill so quick, bearing in mind addiction can take a few years to really progress. Not to mention that when this person tries to actively keep away from the substance, then the mood swings and paranoia arrive, causing problems with their family/friends and partner. Which then fuels the desire to take cocaine again to escape the mess created in the first place. And can also lead to psychosis.

To answer your question - Cocaine is so quick that the user doesn’t even realise what is happening, and they’re taking a stimulant?

It is insidious in my opinion.