Side Mission: Fast
Start this drug-fuelled odyssey at Aubrey's Diner, southwest of the giant statue in Faith's Region.
Talk to the guy going through the garbage. He turns out to be your contact, Tweak. Speak with him to start the mission for a refinement of the Fast formula. This mission feels like it was originally written to give you access to Fast in the first place, but now it simply reduces the crafting components required.
You will need some components to continue. If you don't already have them, the HUD will tell you where to get more. You do not need to use any storage space perks to carry the requisite ingredients. If you find yourself short, there are some supplies in the bunker out back (east) of the diner.
There's also a pretty good answering message from Zip down there.
When you have the required stock, catch up with Tweak at his playground, southeast of the Hope County Jail.
Talk to Tweak again (sigh), and he'll set you on an obstacle course. Just follow the arrows and do as he says. It's very easy, but remember the motions- you'll be doing this later on a timer.
Once you've murdered the dummies and brutalized a pig or two, talk to Tweak in his lab.
Return to the course, and grab a syringe from (no doubt fully sterile) bedpan.
Queue up a dose of Fast from the utilities menu, via the weapon wheel.
Run through the course again. You've got way more time than you need, and most of that will be spent killing the pigs.
Talk to Tweak when you're all done to complete the mission, score $800, and get a reduced component recipe for Fast.