excerpt from GHB FAQ @

http://leda.lycaeum.org/Chemicals/GHB.703.shtml

1-4 g.
A typical "recreational dose" is 1.5-2.5 g
3-4 g will induce sleep
>5 g is an overdose that can dangerously suppress respiration.
At a sufficiently high dose, GHB can cause CLONUS, a rapid, rhythmic contraction and relaxation of muscles which would be better described as muscle spasm or uncontrollable twitching than a seizure. GHB can also cause intense drowsiness, abrupt sedation, and deep sleep which is probably better described as unarrousability or deep sedation than coma.