If by loose, you mean totally wiped out maybe because of bankruptcy, it isnt recoverable.
This happened to me with WorldComm stocks and bonds. The company reported fraudulent earnings, got caught, and went BK. I received nothing for my stocks and maybe 10% of the bonds. I declared the losses on my taxes the following year.
If by lose, you mean the stock price dropped a lot but is still operating, you have to make a choice. Was the loss due to market conditions or the company itself? Today, April 6. 2018, many stocks were hurt when the indexes dropped by 2% or more. Good companies will recover. If you cant stomach the loss, sell the stock and recover what you can.