As a former EMT self medication is legal dependent upon your state laws. Texas allows self medication as long as the meds you are pushing are legal. Luckily, I have a prescription for HGH due to a low insulin growth factor on my blood work so I just told them that the injection site for the HGH was infected. The doctor called in a script for ciprofloxacin and all is good to go. USMC is correct though you shouldn't lie to the doctor, antibiotics for a spider bite may interact in a bad way with something else you may be taking i.e. steroids. It is better to tell the doctor that you would like to have doctor/patient confidentiality and explain what really happened. He, by law, can not write it down or tell anyone else, including the insurance companies, that you had self medicated with an illegal substance. He will definitely give you a stern lecture, haha, but that's about it.