Amino Acids
Amino acids are cheap, well-tolerated building blocks, and a few have solid trial support for a specific, narrow use — glycine and sleep onset is a good example. Others are marketed on broader claims than the evidence currently supports. As with the rest of the site, the grade on each product is doing the real work here, not the ingredient's general reputation.
4 products · sorted by evidence grade
Common questions
Which amino acid supplement has the strongest evidence?
Nothing in this category reaches grade A — glycine, taurine, l-glutamine, and HMB all top out at grade B for their strongest claim. By evidence robustness, taurine (B) arguably leads: a 2024 systematic review and meta-analysis pooling 20 RCTs (808 participants) found it lowers systolic blood pressure by roughly 4 mmHg, with the biggest effect in people who are already hypertensive; cardiovascular trials typically used 1.5-3 g/day. Glycine (B) has clean but smaller RCT evidence for sleep — 3 g before bed improves subjective sleep quality and next-day alertness — though those trials are small and come mostly from a single research group, which is why it isn't a stronger grade. L-glutamine (B) and HMB (B) also earn a B, but only for specific stressed populations (critically ill or post-surgical patients for glutamine; older adults for HMB) rather than for healthy people.
Do amino acid supplements actually help you build muscle if you already lift?
For a healthy, already-trained lifter, the honest answer is mostly no. HMB is a solid grade B in older adults but drops to grade C in young trained athletes — a 2018 meta-analysis found no effect on strength or body composition regardless of dose. L-glutamine's muscle-recovery/soreness claim is also only grade C, with systematic reviews finding no consistent benefit in well-nourished lifters. Taurine may modestly reduce exercise-induced muscle damage, but the evidence is mixed and its real grade-B strength is cardiovascular, not performance.
When the evidence changes, we’ll tell you.
One short email a month. New A-grades, downgraded claims, and reader questions.
Medical disclaimer. The information on this site is provided for educational purposes only and is not intended as medical advice. It does not constitute a diagnosis, treatment plan, or recommendation for any specific health condition. Always consult a qualified healthcare professional before making changes to your supplement regimen, diet, or lifestyle — especially if you are pregnant, nursing, taking medications, or managing a medical condition.
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