I think it happens when you hit a blood vessel. I am on Avonex and have had bruises

Make sure you're going straight in with the needle I've found this lessons the bruising!! Still get some on my legs but I think it's bc the leg muscles are harder than the rest!

Yes. I get them as well at times. If you have an auto injector adjust it so that the needle is shorter that should help. I hate this medication because of the side effects. :( Hope I was helpful.

What is your needle set on.. I was told 6 is the number it should be set on.. Where did you shoot yourself?

I am on copaxione and have experienced a slight bruising at the injection site. it has only happened a few times and so far has caused no problems.