When House learns there is a new drug that has actually re-grown muscle in animals, he goes to Dr. Riggin's lab, ostensibly to find out about it's clinical uses, but really to steal some to try on himself. In The Fix, Dr. Riggin tells him how well the trial is going, and that because the drug is processed well by the kidneys, it should not be toxic. House gets Riggin out of the room and steals more of the drug.
Later in the episode, Riggin looks in one of his cages to find out a rat has died.
House loses his drug in an accident when he suffers a sudden leg cramp. However, his pain has lessened and his leg has been getting much stronger, so in After Hours he goes back to the lab to get more of the drug. When he gets there, Riggin is cleaning out the lab to start a new trial. When House asks when Riggin is about to get his Nobel Prize, Riggin tells him that unless there is one for rat poison, it's unlikely. He tells House all of his experimental subjects developed tumors. House asks if there were any indications that anything was wrong, and Riggin mentions that some of the rats were suffering from cramps, but there were no other signs.