It is possible that your insurance company can send an EOB to the primary enrollee of your insurance. An EOB is an Explanation of Benefits (EOB) that your insurance company sends out that show the basic information about anything your plan helped cover during that statement period, from prescription costs to hospital payments
To prevent this from happening, you can call your insurance company and ask them to send the EOBs directly to you and to not share it with your parents. All you would need to do is call the number on the back of your insurance card and say, “Hi, I am 18 years old and still on my parents’ insurance plan. I’d like to have my EOBs sent only to me.” Of course, each insurance varies on the information that they include on the EOBs and its possible they won't include this medication. --but this can't be guaranteed unless you give them a call.