Get real people, if people outside the Akamachi clan know about the pills, it's no longer a secret. Especially if the pills have been around for decades. If choji and shikamaru are good friends and that's why shikamaru knows then from the same premise it would be suffice to say the shikamaru's father knows too becuase choji's father and shikamaru's father are good friends.

Remeber the old rule: Two can keep a secret, if the other one is dead.