Will long-term use of betamethasone increase hair growth to fill in my sparse thin eyebrows?

Betamethasone is not meant for hair growth.  Long term use on the eyebrow will not grow hair.  Instead you may have adverse effects from the long term use.  Please follow up with your doctor on why you are using a steroid medication on the eyebrows.

Without see your eyebrows up close and knowing more about your history, it is not possible to know your diagnosis and recommend treatment. Here are some general points for anyone using betamethasone around the eyebrowsbetamethasone is primarily a medication to stop inflammationIf inflammation has something to do (directly) with hair loss, there could be mild benefit but it depends on the diagnosis. There are few hair conditions whereby use of betamethasone helps eyebrow growth.  Betamethasone is primarily designed for short term use not long term. Anyone considering long term needs to speak to their doctor. Long term use of steroids around the  eyes can lead to skin thinning, and rarely changes in eye pressures and cataracts. One needs to be carefully followed. All in all, among the 100 or so causes of eyebrow loss, very few benefit from bethamethasone use. Most causes do not benefit but check with your physician for a diagnosis.  In those that do benefit, use if betamethasone is short term and best conducted under strict physician supervision. 

This drug is a steroid and is used to treat inflammation. It will not regrow eyebrow hair unless the eyebrow hair loss is due to inflammation. Although it might reduce inflammation, once the eyebrow hair is lost, it usually does not return but if the area is inflamed, then it would reduce the inflammation. .