The medical literature is reporting that multiple uses per day is not a problem as long as you don't have some pre-existing heart problems. Your doc is being very (excessively??) cautious.
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HERE ARE TWO MAJOR DOCUMENTS WITH RECOMMENDED TREATMENTS FOR CLUSTER HEADACHE, ONE FROM A U.S. PHYSICIAN, THE SECOND FROM EUROPE.
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Here is a link to read and print and take to your doctor. It describes preventive, transitional, abortive and surgical treatments for CH. Written by one of the better headache docs in the U.S. (2002. Rozen)
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Treatment guidelines from Europe
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A. May, M. Leone, J. Áfra, M. Linde, P. S. Sándor, S. Evers, P. J. Goadsby:
EFNS guidelines on the treatment of cluster headache and other
trigeminalautonomic cephalalgias.
European Journal of Neurology. 2006; 13: 1066–1077.
Download free full text:
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(Thanks to "cluster" for link.)