Since you are European citizen under doctors medication you have any right to take your prescription drugs in your journey to Thailand.
If you want go to interprenders to translate your medical prescription drug in order to avoid any stupid wise guy from tax authorities to pay taxes for your health.....
If Thai Tax Authorities insist to pay taxes for your prescription drug then call Royal Thai Police to register the event and take their report number of registration.
Do not shout ar cry but to be polite explaining them that your drugs are for your own life!