How to git gud at being a crippling drug addict.
Everything is temporary. Use items whenever possible, as your inventory tends to fill up quickly. As the investment banker, you don't have much time for inventory management. You might even discover that some tools are better than you thought.
Don't be afraid of shoving that black poisonous needle in your arm. Try to find a toilet before injecting yourself, if you have the time.
Gas fumes and effect ponds can combat withdrawal. You should only use them as a last resort, though.
Antidotes are your friend. Antidotes will negate all harmful effects, and you can stave off withdrawal with no consequences. They even neutralize the effect of poison ponds and gas fumes. The antidote itself does not prevent withdrawal.
Cigarettes pause the withdrawal timer. Nicotine only deals 10 damage when you use it and has no lasting damage, so if you have the health to spare it might be wise to smoke. (But not in real life.)
From 4-1 and onwards it gets pretty hard to find drugs. Try to stock up beforehand, uptown is particularly grueling.
Bully scientists. Jocks, gorillas, and investment bankers all share a burning hatred of scientists. They're one of your best bets for finding syringes, along with drug dealers and trash cans.
Buy out drug dealers' supplies. All of it. Even the bad stuff. Don't be a picky drug addict.
The investment banker has similarly frenetic gameplay to the DOOM guy. Except DOOM guy doesn't have any anxiety, only unbridled wrath. You have to be fast, efficient, and creative. You also have to think quickly, as you'll be making a lot of split-second decisions. Make sure you're ready to mash the F key during combat, although that applies to any character.
This class depends heavily on the environment. If you're a new player, you should get a feel for the game and its mechanics first, or you might wind up resenting this class and missing out on one of the most fun classes (in my opinion).
Opinion: Don't remove Addict with an augmentation machine. The game is way more fun when you feel like an actual drug addict. Plus, it encourages faster and more efficient gameplay.