The album "The Uplift Mofo Party Plan" was released in 1987. It was the band's most successful so far. The album entered the "Billboard" 200 chart, but only at number 148. During this time, Kiedis and Slovak had problems with drugs. Slovak died on June 25, 1988. Because of this, Irons left the band. He said that he did not want to be part of a band where his friends were dying. Kiedis and Flea agreed to keep going with the band.