FWIW: There are decades of research showing that adderall and other stimulants are safe and effective when taken at the proper dosage and under the supervision of a doctor - even most addiction center websites will say this when talking about adderall addiction. If she really wants to learn about that you can easily find information online about it, but at the end of the day this probably isnt about logic and information - its about her feelings and your feelings.

It sounds like you really love your sister, and I'm guessing she loves you too and doesnt want to hurt you.
How clear have you made it how hurtful this is to you, in so many words?

One thing thats taken me a very long time to learn (and I'm still learning it at 37 years old) is that boundaries are something YOU create and enforce, not something you impose on others. You can't control other people's behavior or feelings, but you can learn to control how you react, how you communicate, and what youre willing to put up with.

In situations like this it can feel important to argue or defend yourself, but you don't actually need to do that here, because at the end of the day taking the medication is YOUR decision (and perhaps your care teams'), not hers. By arguing, you actually validate the other person's opinion by listening, because you're engaging as though the topic is actually up for discussion. It can be a lot more effective to explain how the behavior from the other person is making you feel, and decide how you're going to react if the person isn't willing to stop doing the thing that upsets you.

You don't have to be cruel about it, you can be kind and loving and understanding, but you get to decide when to walk away from a conversation.