For filling DS 160 form, what to answer for "have you violated any law for controlled substances?"

Have you violated any controlled substances laws? The question does not ask if you were convicted of any controlled substances laws, but rather whether you have violated the law. You can violate the law without being convicted. A violation of a controlled substances law would most likely result in a denial of your visa application. You can read more about nonimmigrant visas at http://myattorneyusa.com/nonimmigrant-visas.