Punishments for falling foul of the law can be severe, so you should err on the side of caution

Traveling with Medication
When it comes to taking medication while travelling, it is best to err on the side of caution rather than regret. When you travel with something that is prohibited or restricted in the country that you are visiting, there is a possibility that you will be questioned, that your medication will be thrown away, and that in some extreme cases, you may even end up in jail. It is highly unlikely that you will get in trouble for bringing in small quantities of medication for personal use, especially if you can provide evidence that the medication is intended for personal use. However, it is essential to plan ahead and execute the necessary steps in order to guarantee that the things you pack in your suitcase won’t cause any problems during your trip. Since Brexit, the regulations regarding travelling with conventional medications have remained unchanged, which is a relief because these regulations are already quite complicated. Even finding clear information online is more difficult than you might expect, which is concerning given how much is at stake if you make a mistake. Here is the information that you require.
Leaving the United Kingdom while carrying medication
Your first priority should be to ensure that you are in compliance with the Misuse of Drugs Act 1971 of the United Kingdom, regardless of which country you are visiting. When leaving the UK in possession of medication that contains a controlled drug (for a list of the most commonly found controlled drugs, visit the website of the gov.uk), you are required to be able to demonstrate to the UK authorities that the medication is for your own personal use by providing a prescription or a letter from your treating physician.
At least one month in advance of your trip, make an appointment with your primary care physician or visit a travel clinic.
Make an appointment with your doctor well in advance of your trip if you think you might require an official letter, or if you want to discuss other health requirements related to your trip, such as getting immunizations, malaria tablets, or additional supplies of prescription medication. Even if you don’t typically pay for prescriptions, you should be aware that the National Health Service (NHS) rules prohibit the provision of more than a couple of months’ worth of medications at a time. Even in the current climate, when many travellers are likely to be planning trips at short notice in order to stay on the right side of changing restrictions, you still need to make sure that you are well prepared in advance.
Check to see if you are required to have a personal licence.
You are required to submit an application for a personal licence with the Home Office if you intend to travel outside of the United Kingdom for a period of three months or longer and are transporting sufficient quantities of any prescription medication to last for that duration. Carry out these steps at the very least 15 calendar days in advance of the date you intend to travel.
Keep your medication in the container it came in and bring a copy of your prescription with you at all times.
This will be helpful in persuading border officials to let you pass, but keep in mind that some countries may require additional documentation, such as a letter from your primary care physician. Before you ask for a medical certificate, you should check with the embassy of the nation that you will be visiting because some medical practises charge for them and because they are a time drain for general practitioners. Generally speaking, a print-out of your medical summary is sufficient, as long as it is rubber-stamped, signed, and dated, as recommended by Dr. Jane Wilson-Howarth, a general practitioner who is also the author of three travel health guides. In most cases, this service is offered at no cost by general practitioner surgeries.

Medication
Commonly subject to regulatory controls
There is a significant amount of variance in the regulations that govern bringing medication into another country depending on where you are going; however, there are some classes of drugs that are typically prohibited everywhere. These are the following:
Codeine or medication that contains codeine, such as over-the-counter medications like Nurofen Plus and Solpadeine that contain codeine as an active ingredient. It is possible to be arrested in a number of countries, including Thailand and the United Arab Emirates, for bringing codeine through customs without prior authorization.
Powerful painkillers derived from poppy seeds, such as morphine and tramadol Plus, all of the following are among the categories of medication that are restricted in a lot of different countries:
Opiate painkillers
Antidepressants
Sleeping pills
Medication for the treatment of anxiety (including diazepam)
ADHD medication
Cannabidiol
If you intend to travel anywhere with any of these items or with medical equipment such as syringes or an EpiPen, you should exercise an increased level of caution, as it is highly likely that you will be required to present some kind of written permission.

Travel Medication
Countries with stringent regulations concerning medical treatment
Greece
You are permitted to travel with up to five different prescribed medicines for personal use; however, you are only allowed to take a maximum of two boxes of each medicine. If you need to bring more than the allowed amount, you will need to check with the Greek National Organization for Medicines upon your arrival to see if you need special permission. Because Greece classifies codeine as a controlled substance and requires a prescription for its use in any circumstance, it is illegal to bring into the country any medications that contain codeine but were purchased legally over the counter in another country, such as the United Kingdom.
Japan
In order to bring more than a personal supply of non-narcotic medication into Japan with you, you are required to obtain a Yakkan Shoumei import certificate before you travel. This certificate can be obtained online. Regardless of the quantity, if you want to possess drugs that Japan considers to be narcotics, you are required to obtain permission from the relevant Narcotics Control Department in Japan. Codeine, diazepam, and pseudoephedrine are some of the substances that fall under this category. Some nasal decongestant sprays also contain pseudoephedrine.
Mexico
You are permitted to bring any prescription medication into Mexico for your own personal use, regardless of the active ingredient; however, you are required to present a significant amount of documentation. You are required to have a prescription or letter from your primary care physician that details the quantity of medication you will require during your stay, the daily dose, and the quantity of medication you will bring into the country (which cannot exceed the quantity of medication you will require for your stay). In addition to this, the prescription needs to be translated into Spanish, which further complicates matters.
UAE
When compared to other nations in the Middle East, the United Arab Emirates is known for having the reputation of being one of the countries in the world with the most stringent policies regarding the importation of medication. It takes a zero-tolerance approach to drug-related offences, so before bringing in any medication that is on the UAE Ministry of Health’s list of controlled substances, make sure you check the website of the UAE Ministry of Health and ask for permission to do so. This includes headache tablets like Exedrin, arthritis medication like Tylenol, and mint lozenges like Niquitin, as well as skincare products, herbal medicines, and opiate painkillers derived from poppy seeds, not to mention poppy seeds themselves.