Minecraft 14w32d, Minecraft 1.8
OS: Mac OS X 10.8.5
Processor: 2.5 GHz Intel Core i5
Memory: 4 GB 1600 MHz DDR3
Java: 1.6.0_65 (64 bit)
When typing /help effect or just /effect, the game brings up the correct syntax in the chat, which reads:
/effect <player> <effect> [seconds] [amplifier] [hideParticles]
The <effect> argument also has another option, which is 'clear':
/effect <player> clear
which will clear all of their effects.
This option is not shown in the help syntax, and this other option should be shown.