This chapter of the Vampyr Game Guide describes the craftsmanship and drug development process.
How to craft and improve weapons?
There is quite a simple crafting present in the game. Among other things, you can improve your weaponry by unlocking new skills and enhancing damage levels.
Additionally, you can create drugs for the residents at your desk and create serums that serve as specific concoctions, renewing, for example, the hero's health level in combat.
In order to create better items, you need fragments of a good trigger or fragments of a good handle. These are available with later missions - merchants gain a new assortment and enemies have a better loot.
Recipes and medicine crafting
The same is true for new medicines - at first you can create only the basic ones. As the plot progresses, you'll get new recipes. You will get the first set of new drugs, for example, during your search in the basement of Old Morgue.
In the game you can find a lot of different rubbish and seemingly useless items - just collect the leftovers from enemies or open all the boxes. However, if you go to the safehouse, you can use the items you gained as a craftsmanship materials.