Serum

Any orally-administered mutagen can be concentrated into a higher-powered serum. Researchers in the Lab discovered that this gave them more bang-for-the-buck when administering the mutagen, at the cost of significantly higher demands on the subject's system. There were unconfirmed reports of significant behavioral side-effects in subjects exposed to significant amounts of particular serums, though the research in that area was regrettably halted when the Cataclysm struck.

HOWTO Serum

As with mutagens, you'll need a recipe to convert your favorite into a serum. Most sources for orally-administered can help, and there's a recipe-book specifically for serums as well. The process requires Cooking skill 9-10, depending on the base product's level, and cooking the chemicals down takes a while.

Once you've got your serum, you'll need a syringe to inject it. Syringes are not consumed.

In general, injecting yourself will provide you with 1-3 mutations, with an excellent chance of 2 and good odds of all 3. You'll take a Hunger, Thirst, Fatigue, and Pain hit based on the amount of mutations you gained; more mutations means a harder hit. The process is not good for your Health either, so it's good practice to eat some vitamins or shoot up a flu shot afterward.

(Mutagen-writer's warning: Injecting more than two serum-shots at one time is generally a bad idea. Pace yourself!)

Why use serums?

Serums are generally more cost-effective than their associated mutagens, and can take you over the Threshold. Apart from that, several folks on the forum have expressed a preference for oral mutagen, since it's easier to control and has fewer side effects.