Or put some pure theanine powder in your coffee. I use this brand because there is no cellulose or other non-soluble ingredient in the powder that ends up floating on the liquid:

https://www.iherb.com/pr/metabolic-maintenance-l-theanine-20...

I twist the capsule apart, then pour its contents (the powder) out. Buying the powder inside capsules is a convenient way of measuring out a very small quantity of powder.