2, 4 or 6mg of Imitrex all give you the same two hours of efficacy.  The only question is, was the it enough to abort your attack.  In the experience of many here, 2mg is very often enough.

When I have to resort to Imitrex I use the 4mg stat dose kits.  It has never failed to abort an attack for me.

-Dennis-

Rebound headaches. "Rebound Headaches--A Review", Au. John S. Warner, M.D., in HEADACHE QUARTERLY, 10:3(1999). (There is some confusion on the board about the meaning of "rebound". There appears to be an emerging consensus in the medical literature to define "rebound" as a headache which is caused by the overuse of any medication used to abort a headache or relieve pain. "Recurrence" [of a headache] is being used to refer to the redevelopment of an attack when its "normal" duration is longer than the useful life of the medication which has been taken. That is, the medication effectiveness is reducing before the headache has come to an end; the pain redevelops.)
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Sumatriptan has a hard initial punch and relatively short effective life--a combination which works well for most Cluster attacks. However, some people, whose Clusters have a longer life, find that the med is wearing down even as the pain continues. One can understand how this sequence comes into one's thinking: Attack, Imitrex injection, pain continues, it's a rebound cluster which has developed from the Imitrex. In fact, this is a recurrence of the attack, not a rebound.

This is one of the reasons that several other triptans were developed having less initial punch but longer effective life. While aimed at the migraine crowd, at first, a number of cluster users have found this characteristic of value to them.

Joshua wrote on Dec 20^th, 2010 at 1:02pm:

One of the hardest things I've ever had to do, was quit using imitrex, just for this reason and it was one of the best things for me.  Less frequent and intense hits ever since.