The usual dose taken is a single tablet at the time of the attack but if it is not effective in relieving the symptoms a second dose may be taken six hours later. Imitrex without prescription http://www.hawaiianhospitalitygroup.com/ - buy imitrex Imitrex is a prescription drug used to treat migraine and cluster headaches. Migraine headaches can be so severe as to result in lightheadedness, nausea, and vomiting.