How long after starting 20mg Lisinopril should you see a marked reduction in Systolic reading?

You should see a good difference pretty quickly. They may need to add a diuretic to compliment the effectiveness like Hydrochlorothiazide (HCTZ) if the Lisinopril by itself doesnt work. Lisinopril is an ACE inhibitor and I'm not sure if it will have much effect on your migraines unless they are related to the high blood pressure. Beta blockers are usually more effective in preventing migraines-drugs like propranolol, metoprolol, atenolol. I take atenolol, myself, for high blood pressure and I've noticed a great improvement in my migraines. I hardly ever get them anymore-maybe once or twice a year as opposed to several times per month!! You could ask your Dr if he thinks a beta blocker might be more effective, to kill two birds with one stone, per say. ACE inhibitors are the ones that can cause a persistent non productive cough in some people so be on the lookout for that and if it occurs talk to your prescriber.