Depending on the medication, yes, you might do. There are multiple pharmacies in the cities, many open 24-hours a day, but in more rural areas you might need to travel to find the nearest dispensary. Some medications are available only with a prescription from a medical professional, whereas others can be purchased over the counter. It is essential to know whether prescription medications you have taken in the UK are permitted in Thailand. The regulations around drugs are strict, and in some cases, you may need to apply for a permit or be restricted to bringing 30 days worth of supplies with you.