In general, Alchemy is a semi-mystical discipline concerned with trying to attain absolute perfection. The popular misconception of the "Philosopher's Stone" as a substance which turns lead into gold is just that, a misconception. Rather, alchemists are always trying to make a thing more like itself, in hopes of eventually managing to make something a perfect example of whatever that thing is. The "Philosopher's Stone" is that mythical substance which is so perfect that it cannot help but induce perfection in all it touches; turning lead into gold is a popular but ultimately trivial and uninteresting example -- for what would the Philosopher's Stone do to humans? Alchemists have been branded as heretics for suggesting that it would turn them into gods....
Alchemists can prepare herbal medicines and drugs just like a Herbalist can, although they usually don't know how to find the plants, nor much about administring medicine. However, they can also enhance these herbal formulae, strengthening properties the substances already have. This process requires a laboratory, and takes 1d6+4 days of work per batch of one formula; it doubles all effects of the drug or medicine in question. The exact size of a batch varies, but will usually not be much more than ten doses; the fair market price of alchemically enhanced medicines or drugs would at least be twice the normal price (if it was for sale, that is).
The various alchemical elixirs listed in GURPS Magic are different Specializations of the Alchemy skill. In order to make an elixir, you must either have bought it up at least one level, or have a detailed recipe at hand; not all elixirs listed in Magic should be known to Hârnic alchemists, and the Greek/Roman names should be ignored. A suggested list of available elixirs will appear here the day I remember to bring my copy of GURPS Magic to the computer lab, along with suggested difficulty degrees. Making an elixir is impossible in a no-mana area, and takes twice as long in a low-mana area.