Usually a half a cup of fairly weak, instant espresso. Lately I've been increasing it but it doesn't do anything. I'm generally sensitive to caffeine so I dri

Usually a half a cup of fairly weak, instant espresso. Lately I've been increasing it but it doesn't do anything. I'm generally sensitive to caffeine so I drink my usual half-cup over 4-5 hours and sometimes fail to finish it. My genetics indicate I'm a fast metabolizer of caffeine.