Temporary bans are in place for 33 substances including K2, but they will lapse in August.
A select committee is currently working on the Psychoactive Substances Bill which would ban all unsafe synthetic drugs from August.
Coroner Scott says the ban can't come quick enough.
Speaking in relation to Simeon's death, he said synthetic cannabis was "beginning to feature as a factor in some of the deaths I am investigating and I imagine that other coroners are finding this also''.
"I cannot see that it has anything to recommend it and the sooner it is made an illegal substance the better so far as I am concerned,'' he said.
"I cannot say with any degree of accuracy what effect this substance had upon Jarrett [Simeon] but it was almost certainly negative and may very well have contributed to his death.''
While he admitted his knowledge of party pills was limited, he could not see that they are "of any benefit whatsoever''.
The shop where Kahui and his mates bought the legal highs before washing them down with straight rum in Pukekura Park has since closed down, but still sells them online.
Coroner Scott welcomed the shop's high street closure, adding: "To my mind, the sooner such pills or substances become illegal the better.''