"Massage Therapy can lower blood pressure and cortisol (the stress hormone)."
When receiving a massage, it helps a lot of things happen. One of the biggest things that is affected is circulation, which allows your blood to flow more freely, which helps your heart move stuff around more easily, which in turn can help to lower blood pressure. Another thing that can cause blood pressure to rise is too much of the stress hormone cortisol. Cortisol is the "fight-or-flight" hormone that is supposed to help get the body thorough a stressful situation, however our bodies have become so bombarded with stress from so many places and in so many forms, it can stick around and cause blood pressure to to do bad things. Massage releases hormones that can counteract cortisol, and the overall massage environment helps to calm the mind and body, helping the cortisol to not be needed, and helping to flush out the stuff that is already there due to the increased circulation.
As with any massage - while it can help with some medical conditions, massage therapy should in no way replace a doctor's orders including medications or other treatments. Massage can not replace medical treatments, but it can help as another tool to help treat conditions, and perhaps help to make other medical treatments less needed. Do not replace anything recommended by a doctor with massage therapy, but the doctor can be clued in to help see if and how massage can help.