2xH2O2 => 2xH20 + o2
Basic chemistry. It'll make you burp, but there is nothing there that can affect BP.
If still in doubt, ask a Dr. and he'll tell you the same.
My concern would be for damage to the stomach lining, and at three percent solution I do not see problems with free radicals. I also suspect the doctor's comment is based on you possibly up-ending the bottle, and as he would tell you, H2O2 generating water and O2 gas in your belly cannot have any theraputic (helpful) value because there is nothing there that can help.