Thanks [...] for helping with the 2mg/mL with a mark for giving 0.5 mg.
So for the two methods I gave, the top one is still use 200 mL of water and drink 40 mL to get 0.1 mg.
But for the "HOWEVER" version, the forth step would change to become:
(4) Use your 10 mL syringe BUT ONLY GIVE YOURSELF 5mL to get 0.1 mg of drug.