I found a couple of webpages with more information. One is by U.S. Customs and Border Protection, for people coming into the US. Their recommendations:

• Declare all drugs, medicinals, and similar products to the appropriate CBP official
• Carry such substances in their original containers
• Carry only the quantity of such substances that a person with that condition (e.g., chronic pain) would normally carry for his/her personal use
• Carry a prescription or written statement from your physician that the substances are being used under a doctor's supervision and that they are necessary for your physical well being while traveling

The other is Medications and International Travel, a "tipsheet" by Mobility International USA. It's all about... traveling with meds.