1. Understand Controlled Medicines: Controlled medicines include drugs that have a high potential for abuse or addiction, such as certain painkillers, stimulants, and sedatives. The UK and many other countries consider testosterone to be a controlled substance. Every country has its own regulatory lists and regulations.
   
2. Research and Compliance: Before traveling, research the medication laws of your destination. Some countries have strict rules about bringing in certain medications, especially controlled substances.
3. Proper Packaging: Keep medications in their original containers with clear labels. This helps customs officials verify them against your documentation.
4. Quantity Restrictions: Be aware of the quantity of medication you're allowed to carry. Some countries limit the amount you can bring without a license or special permission.
5. Customs Declaration: Declare your medication at customs if required. Non-declaration can lead to legal issues, even if the medication is legal in both the origin and destination countries.
6. Carry Documentation: Carry a copy of your prescription (and consider translating it into the relevant language). If you need a letter to help verify the legitimacy of your prescription, you can obtain one through the Treatment Recommendation request form on the GenderGP website. Simply tick the box on the bottom of the form for the "Travelling With Medication Letter", which costs £30.

Lastly, always consult with specialists and check with the relevant embassies or health departments for the most accurate and updated information regarding your travel with medications. Even if your medication isn't a controlled substance in the UK, it might be one in your country of destination.