How soon after Juvederm injections in my lips can I use my Flex-Away, a mouthpiece used to exercise the facial muscles?

Follow your injector's instructions. If you have substantial swelling and bruising, it's better to wait until it goes a way a bit before exercising.

Filler that is placed in areas of high mobility (e.g.
lips) will not last as long as filler placed in more static areas of the
face (e.g. cheeks). This is because the muscular activity causes the
product to spread out more diffusely over time from its desired
location. If you purposely move your face with exercises, the results
will certainly be shorter lived.  Additionally, facial exercises can actually cause you to develop more wrinkles over time.  I'm sorry to be down on your device, but I do wish you well!

I would recommend waiting 3 days after a lip injection before using Flex - Away, this allows the product to settle. Fillers to the lips are often metabolized quickly due to constant movement. Flex - Away may contribute to dissolve product.

Each injector will have different guidelines for post treatment care. Many injectors will be fine if you continue using the mouthpiece 3 days to a week post treatment. Consult with your injector as he or she knows the specifics about you and the scope of the procedure.

Filler injections into the lips and around the mouth don't last as long as other locations because they move more. So, if you are amping this up even more by using special mouthpieces designed for additional facial exercises, you should know you are most likely going to dissipate the product even faster..... With that being said too, know that it's not a matter of lack of muscle movement that causes wrinkles and sagging - it's an actual loss of volume. Facial exercises don't create volume. They just move muscles. "This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."