Negative Effects of Preworkouts

Preworkout supplements are one way for weight lifters and fitness fanatics to get energized for high-intensity workouts. The stimulants in these supplements provide a boost for your muscles and energy level, but they can also lead to a number of negative side effects including dehydration, kidney problems and high blood pressure.

Preworkout Supplements

Preworkout supplements are mostly composed of stimulants such as caffeine and creatine, and usually come in powder or pill form. These stimulants are highly popular among weight lifters, according to the University of Maryland Medical Center, for their ability to increase muscular endurance and power while postponing muscular fatigue.


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When consumed in large doses, preworkouts can cause dehydration. The two most common ingredients of preworkouts, caffeine and creatine, are both diuretics, meaning they cause you to urinate more frequently than you would normally. Additionally, creatine causes the water in your body to be drawn into your muscle tissue. While that may give the appearance of larger muscle mass, the water retention in the muscles draws water away from other parts of your body, further increasing the risk of dehydration.

Kidney Damage

Taking high doses of creatine over an extended period of time can cause kidney problems. Creatine is a natural product your body produces and stores in the muscles, but too much additional creatine can not only cause your system to stop producing its own creatine, but can also lead to an increase in production of renal by-products such as creatinine. While creatinine in small doses is safe, in large doses it can aggravate existing kidney problems, leading to possible renal failure.

High Blood Pressure

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Like all stimulants, caffeine and creatine can cause a dramatic increase in your blood pressure levels. Because high-intensity, short-duration exercises such as weight lifting already raise your blood pressure, taking excessive amounts of caffeine right before lifting weights can cause a potentially problematic spike in your blood pressure levels.

Other Possible Effects

Although dehydration, kidney issues and high blood pressure are the most common negative side effects of preworkout stimulants, there are many other possible side effects that can affect certain individuals. These can include uncontrolled muscle movements, headaches, weight gain, cramps, upset stomach, nervousness, insomnia, diarrhea, nausea and dizziness. Additionally, since preworkout supplements are classified by the FDA as food rather than drugs, they are not subject to the same strict standards and regulation as medicine. Consult your doctor before adding any supplement -- preworkout or otherwise -- to your regular diet.