These include insomnia, nausea, increased heart rate, drowsiness, headaches, anxiety, and jitteriness or restlessness ( 4 ). What's more, many pre-workout supplements pack high amounts — up to 500 mg of caffeine per serving.

Why does pre-workout make you tired?

Caffeine is a stimulant that's found in most pre workout supplements. It increases your energy by binding to the adenosine receptors. Adenosine regulates the sleep-wake cycle. When levels of this neurotransmitter increase, you feel sleepier.

Do pre workouts actually give you energy?

The bottom line

Pre-workout supplements are primarily used to enhance physical performance and energy, but research doesn't back many of their supposed benefits. Although certain ingredients may boost your results, there's no standardized formula and several potential downsides.