IR niacin is in and out of your system quickly, allowing your liver to recover from dealing with it. The
SR hangs around so your liver must deal with it
for extended periods of time, not giving it much time to rest.
Obviously, you can already handle the IR so why subject your liver to the SR?
I bought some SR niacin but after doing some research and finding out about its effects on the liver, I wish I'd bought the IR.