It can take around three months to determine effectiveness. It will take about 30 to 60 minutes for you to notice the effects of propranolol. Propranolol Side Effects And Interactions And How To Avoid Them It will take several weeks to see enough changes in your symptoms to decide if. How long does it take for propranolol to work for migraines . Those using propranolol for anxiety should plan to take their dose an hour or so before they wish to feel the desired effect. After about a month and a half it was working great! My neurologist prescribed 20 mg of propranolol at night and 20mg in the morning. It's worth it for the decrease in my headaches though! Beta blockers reduce the frequency of migraine attacks in 60 to 80 percent of people. The only down side for me is feeling exhausted pretty early into a work out. It usually takes between 30 minutes and one hour to experience the effects of propranolol. Hi i take propranolol for migraine and anxiety, and i fou...