Yes, you are fully permitted to bring prescription and over-the-counter medications into Disneyland and Disney California Adventure. This includes medically necessary items like EpiPens, insulin, asthma inhalers, and antihistamines. When you go through security screening, simply inform the Cast Member that you have medically necessary items in your bag. While not strictly required, keeping prescription pills in their original pharmacy containers can help expedite the process if there are any questions. If you have medications that require refrigeration (like certain types of insulin), you can store them at the First Aid station located near the end of Main Street, U.S.A., or in the Chamber of Commerce at Disney California Adventure. Disney's goal is to be as accommodating as possible for health needs, so you won't face any issues as long as the items are for personal medical use.