Tonics in Taiwan
Walking into a drugstore in Taiwan, you immediately have access to many kinds of tonics, like drugs for a cold, for diarrhoean, for sore muscles and so on. Taiwanese people do enjoy taking medicines, especially without doctor's approval. Working like an elixir, they probably regard the tonics as an useful tool.
Tonics is a bit formal. Usually we would say 'drugs' or 'medicine'.
Medicine is uncountable. "There was a lot of medicine" or "There was two types of medicine"
It should be 'a useful tool' instead of 'an useful tool'. This is because the 'U' in useful makes a 'y' sound, which is not a vowel. This also works the other way, for example, 'an hour'. 'h' is not a vowel, but it sounds like one here.
hope that helps :)