E=mc2Energy and matter are the same. Alchemy users knew this fact centuries before Einstein proved it with modern physics. They also know that the power it takes to pull on a Branch is another form of energy. Done right, this means that any magical energy can be turned into a thing or change it. Making lead to gold means releasing the energy in one metal and using it to form the other. Many uses for this power includes either working with large amounts of matter. For instance, some pull on this Branch to turn useless objects into valuable materials in order to make money. The danger is that the more material affected, the higher the risk of Thorns ripping at the user. In fact, Thorns might hide inside the creation itself. More than one magic-user has found themselves having their friends die from the monsters coming from their fancy new gear.
ThornsPulling on any Branch means a risk of being injured by the Thorns. For Alchemy this often means uncontrolled releases or absorption of energy. A potion might result in a firestorm that engulfs everything nearby. A hardened metal might freeze and cover everything in thick ice. There is a reason for the archetypical explosion in an alchemist lab. There are some examples where the Thorns have cut the user up and turned their body inside out. Sometimes without killing them, only causing excruciating pain. In at least one case, a potion resulted in the practitioner melting and becoming a sentient goo unable to do anything but feel themselves thinning out.
Any use of alchemy depends on the change in matter or energy, which is often accompanied by flashes or sudden darkness as light is emitted or absorbed to feed the process. Instead, there might be heat, byproducts, or the destruction of nearby things. You can't get something from nothing and you can never completely destroy anything. Balance is always maintained, no matter what you do.