What to do when Mother won't take no as an answer?

Our loved ones can get obsessed on some things. One thing my mother gets obsessed about is laxatives. She's not content with something like Miralax. She wants the heavy duty X-lax, which as you know is not good for her. She thinks if she doesn't use the bathroom each day, then she needs a laxative. I tell her no. She follows me around the house, pleading first, then yelling at me. I often end up having to leave the house. Laxatives make her stay up all night pooping, cause a mess in the bathroom, and sometimes blow out in other areas of the house.

This evening I said no. She'd been to the bathroom many times this week. I really believes that for some reason she just likes to take laxatives. It puts me in a spot, like letting her do something she wants to do, even if it is bad for her and causes a mess.

I guess what you could say she is doing is bullying me into giving her laxatives. I don't like being bullied. I like to be able to say no and have it mean something.

What would you do in this situation if your mother liked to take laxatives? Would you just give in and let her do what she wants? Or would you hold off and go through the bad mouthing trying to make you cave in? My mother is nearly 90 now, but no where near death as far as I can tell.