> This argument is so silly against reality, and already, almost nobody understands the things they put in their body to any significant degree, beyond the effect produced.

While the biological effects of any particular chemical still require a great deal of trial and error to determine, drug chemistry itself is unambiguous. Pharma companies employ expert chemists and chemical engineers. They don't manufacture drugs just by randomly mixing together chemicals. At the very least, they must understand what they are making thoroughly enough to determine its physical properties and design a reliable and commercially viable manufacturing process.