CA Health & Safety Code Section 11709

(a)

Two or more persons may join in one action under this division as plaintiffs if their respective actions have at least one market for illegal controlled substances in common and if any portion of the period of use of an illegal controlled substance overlaps with the period of use of an illegal controlled substance for every other plaintiff.

(b)

Two or more persons may be joined in one action under this division as defendants if those persons are liable to at least one plaintiff.

(c)

A plaintiff need not participate in obtaining and a defendant need not participate in defending against all the relief demanded. Judgment may be given for one or more plaintiffs according to their respective rights to relief and against one or more defendants according to their respective liabilities.