Magnesium sulfate / potassium sulfate / sodium sulfate
"This is my second colonoscopy.  The first one, four years ago, had a completely different prep that was pretty easy to handle - gatorade, bisacodyl laxative, polyethylene glycol 3350, magnesium citrate.  Very effective and not too bad.

This time (different doctor and city), they've prescribed a regimen of miralax, magnesium citrate, and suprep.  The miralax and magnesium citrate were fine.  The suprep, however, was the most vile thing I've ever had in my mouth.  

It's not the cherry flavor, it's the sodium in the solution that causes the instant nausea when it touches your tongue.  I managed not to vomit the first prep, but couldn't handle the second.  And this prescription, not covered by insurance, cost over $100."