Someone With Mass wrote...
Nice way to enter the thread, Rip.
There are better (?) ways to turn her down, if you really feel the need to do it.
I think the "I've changed my mind" option at the romance scene is best, as you've already showered her with compliments and expressed your interest by then, he still goes "I just don't want to risk your health".
Sure, it's a shame about all those wasted antibiotics and herbal supplements, and it's still not very nice, but it at least gives hope to continue your relationship later on (Though you can't, not in ME2 at least), when there isn't anything else life-threatening out there.