Isoboromine

Isoboramine (also spelled as isoboromine) is a neurotransmitter in Trill physiology which regulates the connections between the host and the Trill Symbiont. Low isoboramine levels are harmful and may be fatal to the host and/or symbiont, so if isoboramine levels drop below 40%, then the symbiont is removed. This will kill the host, but any joined Trill will willingly sacrifice themselves in order to save their symbiont.

Official records at the Trill Symbiosis Commission state that in 2285, when Torias Dax was in a shuttle accident, he was placed in a coma. He was left in the vegetative state until his isoboramine levels eventually fell below 40% and the symbiont had to be removed. In actuality, the symbiont had been transferred to Joran Belar.

In 2371, Jadzia Dax's isoboramine levels fell dangerously low, when a chemical memory blocker was wearing off in the Dax symbiont. (DS9: "Equilibrium")