Here's what CDC says:
Items to Bring With You
Medicines you may need:
The prescription medicines you take every day. Make sure you have enough to last during your trip. Keep them in their original prescription bottles and always in your carry-on luggage. Be sure to follow security guidelines, if the medicines are liquids.
Note: Some drugs available by prescription in the US are illegal in other countries. Check the US Department of State Consular Information Sheets for the country(s) you intend to visit or the embassy or consulate for that country(s). If your medication is not allowed in the country you will be visiting, ask your health-care provider to write a letter on office stationery stating the medication has been prescribed for you.