When I started finasteride 0.5mg on top of minoxidil 4 mo ago, I lost all minoxidil gains. Should I continue to use finasteride?

Yes, there is initial shedding with Finasteride. It will take up to 6 months to see results. I suggest seeing a hair loss expert now to go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone which can help with hair regrowth and/or hair transplantation. See an expert. Best, Dr. Emer

The suggested dose for finasteride is 1 mg a day. Typically you would want to continue the medication for at least 6 months before making any decision on whether to stop or continue it. When adding finasteride to minoxidil there is typically an additive effect but not a doubling effect.  It is possible to see shedding after a few months but then it should cease. You may want to just continue on with the finasteride by itself at 1mg a day.  Typically finasteride has slightly better efficacy over minoxidil however both are FDA approved to help with hair loss.

It is a good question. Certainly one can get shedding in the first few months of starting finasteride. So in many ways there is nothing unusual about your story. That said, there are many many reasons for shedding so be sure that a physician has re examined the scalp and ruled out all other potential contributing factors. 

If you are under 35, then taking finasteride will have value for you. I don't understand why you lost more hair