Stop Price Gouging Act This bill amends the Internal Revenue Code to impose an excise tax on pharmaceutical companies that sell prescription drugs that are subject to price spikes that exceed the annual percentage increase in the medical care consumer price index detailed expenditure category for all urban consumers (U.S. city average). For each taxable prescription drug, the excise tax ranges from 50% to 100% of price spike revenue received by the company, depending on the size of the price spike and including an adjustment for revenue that is due solely to an increase in the cost of the inputs necessary to manufacture the drug. Pharmaceutical companies must submit specified data regarding drug prices and revenue to the Inspector General (IG) of the Department of Health and Human Services (HHS), and the IG must submit an assessment of the data to the Internal Revenue Service. HHS, upon the recommendation of the IG, may exempt certain drugs from the excise tax if: (1) a for-cause price increase exemption should apply; or (2) the drug has an average manufacturer price of not greater than $10 for a 30-day supply and is marketed by at least 3 other holders of applications approved under the Federal Food, Drug, and Cosmetic Act. The Government Accountability Office must examine: (1) how drug manufacturers and health plans establish initial launch prices for newly approved drugs, and (2) alternative methods that have been proposed for setting the price of new drugs.