It is illegal to sell prescription drugs over the internet in Thailand. Thailand is absolutely notorious for online pharmacy scams where internet 'pharmacy' sites are actually selling counterfeit and contaminated products. There was a scam in 2013, for example, where over 30 different pharmacy websites with different branding were all in fact linked to one woman who was illegally selling counterfeit drugs online in a huge, professional set-up.

You have absolutely no idea what you are buying. It is entirely possible that it is not the drug you think it is, however reputable the website you bought from looks and however genuine all the packaging looks. The ingredients could be toxic or dangerous - that is common in these counterfeit and contaminated prescription drugs. As you have no idea what you are actually taking, they could cause you further harm or interact with other medications or supplements.

Its up to you of course what you decide to put into your own body but this is an incredibly risky and illegal activity, you may well just be throwing your money away and you are endangering your own health. Under the circumstances, is it actually worth that level of risk?