Thank you to all who have replied. I highly doubted this persons statements about Imitrex that it caused pituitary brain tumors and furthermore that Imitrex is only for migraines not for CH's and she had a letter stating so.
However, I just had to research options from the most knowledgeable of all, Clusterheads. and of course the Glaxo Smith Kline (manufacturer of Imitrex) website.
God forbid she was right, then we would all be at more risk than we already are, so I felt it was important to inquire and start this thread.
Below is my reply to her based on info some of you shared here on this thread and what I found on my own...thanks again for your input fellow Clusterheads

Mrs. X, 1st off, no I am not a doctor. I am a Clusterhead of 30 yrs with a wealth of info and unfortunate personal trauma. Secondly, when you wrote that Imitrex is not for CH's and that your pituitary brain tumor was caused by Imitrex, etc it is something to definitely research.
Everybody in this Facebook Group "Cluster Headaches" is here to better themselves and learn more about their disease and be supportive of each other. So by no means am I attacking you personally and am empathetic with your unfortunate medical issues. However, what you wrote is so contradictory to the gains we Clusterheads have made over the years, it had to be addressed. Especially for the newbies who have no idea who/what/where/when/why/etc and are here seeking effective info. God forbid they think they will get a tumor isf they take Imitrex and start doubting their neuro. Again, nothing personal at you, but I am defending Imitrex as a VERY effective treatment for CH's. 'Imitrex (Sumatriptan) is widely prescribed for CH and most docs would be negligent if so.'
Contrary to what you wrote, here are two quotes from Glaxo Smith Kline's website you may find of interest
1. "IMITREX Injection is indicated for 1) the acute treatment of migraine attacks with or without aura and 2) the acute treatment of cluster headache episodes."... See More
2. "IMITREX Injection should only be used where a clear diagnosis of migraine or cluster headache has been established."
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or

'I doubt the manufacturers of the medication would send out a letter to someone stating otherwise.'
'I believe there is some truth to the serotonin statement.'
'As for pituitary tumors they indeed can create a cluster headache mimic but there is no info I can find that trex can cause them. Some research shows the tumors far more prevalent than thought in clusterheads.'
I wish you nothing but the best Mrs. X. Sincere Pain Free wishes to you."