The Adipose Pill Necklace functioned as a portable Inducer. When turned, it activated the Birthing Process of an Adipose within the wearer. They were given away free with every three week Adipose Pill course.
The Doctor attached two necklaces to an Inducer to cancel out Matron Cofelia's Inducer. The Doctor used his and one stolen by Donna Noble. Penny Carter also stole a Pill Necklace. (DW: Partners in Crime)