One thing that some patients have found works, is to get an indwelling pump setup that injects a much smaller dose (often on the order of 1/100th or less of the oral dose) directly into the spine. The pump also does this on a more frequent tiny dose basis. This seems to provide the desired relief, while avoiding most of the other nasty side effects.... Downside is that it's a very invasive procedure and may need to be redone if the body rejects the pump, or other complications occur... Generally it's in the 'last resort' class of treatments that they go to when all else fails...
No idea about how it effects
function, I suspect for most patients they are more worried about other things...It may be worth at least asking about with your medical team, I don't know if there are less severe approaches for folks that are using these drugs for issues that aren't SCI related, but it seems like the sort of thing that might exist... (perhaps similar to the insulin pumps they give a lot of diabetics these days?)
WheelyFixed