I opened and never used a magnesium citrate bottle about 9 months ago ive kept in in my medicine cabinets since then. i am having a colonoscopy and they told me to drink 10 onz of it. is it ok to drink the bottle i have from 9 months ago?

The solution is unlikely to deteriorate and should still be effective. Having said there are more appropriate methods to prepare for colonoscopy, e.g. Polyethylene glycol solution For info: https://www.mayoclinic.org/drugs-supplements/polyethylene-glycol-3350-and-electrolytes-oral-route/precautions/drg-20062627?p=1#:~:text=PEG%2Delectrolyte%20solution%20is%20a,only%20with%20your%20doctor's%20presc