With respect to a 1099-INT and 1099-DIV, what if I have claimed interest every year on an investment that is now worth less money than my initial deposit?

Nothing happens until you sell your investment. At that time, you can claim a loss.

 

The interest you paid tax on would be added to the cost of your investment if it was added to the investment (for example, reinvested dividends).

 

If you claimed the interest every year but cashed it out, then your cost would be your original cost.

 

It’s not clear from your question what you did.

 

Learn more at Topic No. 703, Basis of Assets.