If you need more precision, and if the pill ingredient can allow it 

- dissolve the pill in 100 ml (0.1 litre) of clean water
- in a measuring flask / bottle

then when you need to drink some of it, it will be easy to use exactly only the right proportion. 

Shake the bottle to mix water and the pill ingredient. Drink 50 ml to absorb 50% of the medication.

[![Some measuring bottles][1]][1]


  [1]: https://i.sstatic.net/wdreq.jpg