The Optimum Nutrition (ON) ZMA capsules combine high-quality forms zinc, magnesium, and vitamin B6, which is stated to increase muscle strength, size, and to improve recovery. Each serving delivers 10 milligrams of vitamin B6, 435 milligrams of magnesium, and 28 milligrams of zinc. According to ON, the added zinc provides immune support while the magnesium promotes sleep.
ON has a commitment to quality. Each of their products reportedly undergoes independent and in-house testing for cross-contamination and, in addition, all vendors they use must provide a certificate of analysis for the raw material. While the vast majority of reviews were positive, reporting better sleep and recovery, there are a few users who experienced gastrointestinal issues. A select few consumers also reported a foul smell.