If a business has a loss in its first year or two, the loss can reduce other taxable income (such as from dividends or wages) even if the business expenses leading to the loss included a lot of interest and even if the loan was not secured by your home. The interest on the loan(s) used to start or continue the business is described on the business part of the tax return (schedule C). In most of these calculations the word "deduct" is not used.
If a business is hopeless, you are supposed to go out of (the) business. Insisting on keeping it going despite loss after loss year after year can result in the IRS' treating it as a hobby and after a few years the loss cannot reduce other income. An exception can be made if the business does not "look like" a hobby (such as photography, or raising or racing horses) and it is run in a businesslike fashion and projections for the future indicate profitability.