Weakness and shakiness after drinking coffee can be a sign that you’ve consumed more caffeine than your body can properly metabolize at one time. Caffeine stimulates the central nervous system and can cause shakiness when consumed in excess.There are a few explanations for why caffeine can make you feel weak. Caffeine works by blocking a molecule called adenosine, which acts to depress the central nervous system and makes you feel calm and sleepy. This causes adenosine to build up with nowhere to go. Once the caffeine wears off, the high levels of adenosine may cause you to feel more tired and weak than normal. (6)Caffeine may also cause weakness due to its indirect role in dehydration. It acts as a diuretic, prompting the body to urinate. If you aren’t drinking enough water to offset these fluid losses, you may become dehydrated. Highly sweetened coffee drinks may also play a role since sugar is processed very quickly by the body. It can give you a quick boost of energy, but you may be left feeling even more tired shortly afterwards.