Out of 245 patients admitted to a two-month single-blind phase in a study with propranolol vs. placebo, 148 (72%) were propranolol responders. These responders were randomly assigned to propranolol or placebo for the following double-blind phase. After four weeks, they opted to either (1) remain on the assigned drug for 6 to 12 months or (2) to switch to the other drug for 6 to 12 months. In either case, they then switched drugs for a final one or two months of the study.
No tolerance was found in 80 patients who remained on propranolol for at least six months.
Resurgence of migraine was analyzed in 75 patients who took propranolol for at least six months and crossed over to placebo. Thirty-five patients (46%) continued to show the improvement achieved during propranolol therapy when it was discontinued and only 8 patients (11%) had rebound headaches. No serious complications were noted.