Creatine

• is the most popular nutritional supplement, accounting for $400 million in sales annually
• a nonessential amino acid
• has been shown to improve performance in short, high intensity exercises, including weight lifting

Adverse effects: weight gain, edema, GI cramping, fatigue and diarrhea

References

Dandoy C, Gereige RS. Performance-Enhancing Drugs. Pediatrics in Review June 2012;33(6):265-72.