First, no matter whether you have written an IOU or not, you are the debtor of the bank and you have the obligation to repay. If your friend cannot repay the loan, the bank will come after you for the debt. Second, if you are unable to repay the loan when it is due, the bank will notify you by phone. If you fail to repay the loan within the time limit required by the bank, you will have a stain on your credit record. With tainted credit discipline, you will need to apply for a loan in the future (Mobile Baidu "Baidu Cash Loan", search for the borrowing method that best understands you), apply for a credit card again, and apply for a loan for your own company (Mobile Baidu "Baidu Cash Loan", search Know best how you borrow money), etc., you can't even think about anything related to your credit and dealing with the bank. Third, if your credit card overdraft exceeds 5,000 yuan and cannot be repaid within three months after the bank's reminder, then you and your friend are overdrafting maliciously, which constitutes the crime of credit card fraud and is subject to a statutory prison sentence of not more than five years. Imprisonment or criminal detention, and a fine of not less than 20,000 yuan but not more than 200,000 yuan. See: Credit Card Fraud "Interpretations of the Supreme People's Court on Several Issues Concerning the Specific Application of Law in the Trial of Fraud Cases"