Your pre-workout might also give you a headache, says registered dietician Lonnie Lowery, Ph.D. (via Men’s Journal). In general, this side effect is due to arginine, an amino acid with vasodilating properties. After ingestion, arginine dilates and relaxes the blood vessels in your head (and other tissues), which in turn may cause headaches. Other vasodilators, such as citrulline, may have similar effects.
L-citrulline, a naturally occurring amino acid, is converted to arginine in your body and therefore expands the blood vessels, explains a 2021 research paper published in Applied Sciences. However, both arginine and citrulline support optimal health and may improve sports performance. When used as part of an exercise program, these compounds may delay fatigue and increase your speed, strength, and muscle oxygen uptake. They also have beneficial effects on metabolism, cardiovascular function, and sexual health (per Applied Sciences).
The JISSN states that most pre-workout supplements are safe and have minimal adverse effects. However, some products may contain hormones, banned substances, or impurities. That’s why it’s important to choose a trusted brand and research the ingredients used. Pay attention to the amount of caffeine per serving, too. When consumed in excess, this stimulant may cause nausea, headaches, irregular heartbeat, and other side effects, notes the JISSN. You might also want to check the Operation Supplement Safety (OPSS) database, which features a list of potentially harmful supplements and ingredients, along with practical tips to help you make the right choice.