At 1st level, an alchemist discovers how to create a mutagen that he can imbibe in order to heighten his physical prowess at the cost of his personality. It takes 1 hour to brew a dose of mutagen, and once brewed, it remains potent until used. An alchemist can only maintain one dose of mutagen at a time—if he brews a second dose, any existing mutagen becomes inert. As with an extract or bomb, a mutagen that is not in an alchemist's possession becomes inert until an alchemist picks it up again.
When an alchemist brews a mutagen, he selects one physical ability score—either Strength, Dexterity, or Constitution. It's a standard action to drink a mutagen. Upon being imbibed, the mutagen causes the alchemist to grow bulkier and more bestial, granting him a +2 natural armor bonus and a +4 alchemical bonus to the selected ability score for 10 minutes per alchemist level. In addition, while the mutagen is in effect, the alchemist takes a –2 penalty to one of his mental ability scores. If the mutagen enhances his Strength, it applies a penalty to his Intelligence. If it enhances his Dexterity, it applies a penalty to his Wisdom. If it enhances his Constitution, it applies a penalty to his Charisma.
A non-alchemist who drinks a mutagen must make a Fortitude save (DC 10 + 1/2 the alchemist's level + the alchemist's Intelligence modifier) or become nauseated for 1 hour—a non-alchemist can never gain the benefit of a mutagen, but an alchemist can gain the effects of another alchemist's mutagen if he drinks it. (Although if the other alchemist creates a different mutagen, the effects of the “stolen” mutagen immediately cease.) The effects of a mutagen do not stack. Whenever an alchemist drinks a mutagen, the effects of any previous mutagen immediately end.