I am about half way through my year and a half invisalign treatment. My teeth are getting much straighter.
When I began the treatment, I had a few negative side effects. The first tray was pretty tight so I was clenching my teeth. This in combo with a bit of TMJ caused my jaw to lock shut. Took a few months to completely heal but now it's fine.
Also, I had an horrible lisp for about a month. Now, I only lisp occasionally & most people don't even know I have the trays in.
In spite of the few neg effects, I am glad that I went through with the invisalign.