I was on Avonex for several years. No digestive problems but many flu-like symptoms, worse sometimes than others. I learned from experience that these effects would start 2 or 3 hours after my shot, so I did it at night before bed, after which I took 2 Aleve, since these are long-lasting. The net result was that I'd sleep through whatever the Avonex side effects might be, buffered by Aleve. Though I almost never had to take more the next day, randomly but seldom I'd get sort of a mega-attack that would last most of the next day, regardless.
People's reaction times do vary considerably, though, so I suggest you experiment with timing your shot and taking preventive meds. Do try to do it around bed time, though, so as to minimize the effects.
I now am on Tecfidera, an oral MS med, and after an adjustment period I get no side effects whatever. Like this much better than shots.
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Here are some tips to minimize the flu-like side effects that hit a few hours after a shot:
Stay well hydrated. Drink plenty of water, preferably, in the hours ahead of the shot and afterward. (Of course, it’s not a bad idea to be well hydrated all of the time.) … Use an over-the-counter drug such as Tylenol, Advil, Aleve, etc., or their generics. Take a dose ahead of time, a dose right before bed (if you follow the timing below) and another when you get up in the morning. … Time your injection perhaps 4-6 hours before you go to bed, so you can sleep through the worst period of side effects.
For me and many others, the side effects diminished over time. You’ll eventually forget doses of OTC meds, or you’ll do an injection at a different time, and you’ll realize it’s no big deal. I was pretty rigid about injecting Friday at 5 p.m. or so for several years, but lately I’ve floated between Saturday evening and Sunday sometime, usually getting by with two doses of acetaminophin each weekend. My shot was about 1 p.m. Sunday last weekend, but I was just going to flop on the couch and watch the Super Bowl anyway.
I also endorse having the Avonex out of refrigerator for at least an hour prior to injection, maybe even holding the syringe under your armpit or something to bring it closer to body temperature (don’t use any artificial heat source!).
As for the digestive issues, I can’t link any to Avonex.
Ask questions anytime!