Since everyone uses different amounts, it is kinda hard to say how much.
The best way is starting out with a little and adding more until it is enough.
Starting with about 1/4 teaspoon for a 30ml bottle is somewhere around a good point.
It will also depend on what flavor you are adding to.
If you are sprucing up a menthol liquid, you would probably use less.
If you are adding to a tobacco flavor and want to sweeten it up a bit,
then you could go for just a tiny amount.
The more you add, the monger it may take to dissolve.
But in general, you shake it a few times in a day, and about 24 hours should do it.
If you start to use menthol drops heavily, then you might want to search for menthol drops on ecf. Maybe someone can point out a specific thread with tips and the recipe.
You just fill a bottle with menthol crystals, then top it off with grain alcohol or vodka.
Then to use, place a few drops into a bottle.
