Can I use Retin-A .1% and HA together?

Yes you can combine these without any issues and it does very well for the skin, especially in combination with laser treatments.

The ideal other products to use with Retin-A are an alpha hydroxy cleanser to remove the dead cell build up, an acidic antioxidant like Vitamin C Serum and a zinc oxide sunblock. The first 2 help the Retin-A penetrate to the cellular layer where it can work. The zinc oxide sunblock protects your skin from further damage. None of the other things are doing much for you and, in fact, may be reducing the amount of Retin-A getting to the cells where it can act, thus reducing the effectiveness of it. Topical Hyaluronic acid does not penetrate the skin to interact with the cells and is, thus, a waste of your money. You should make sure that whatever doctor you get the Retin-A from is significantly experienced in skin rejuvenation and discuss what you need with him or her.