Head to head · Amino Acids (BCAA & EAA)
NOW Foods NAC 600 mg Capsules with Selenium vs Optimum Nutrition Essential AMIN.O. Energy
NOW Foods and Optimum Nutrition finish level in our scoring (7.0 vs 7.0), so the right pick depends on what you value most — NOW Foods is stronger on value and transparency, Optimum Nutrition on quality & purity and experience.
Updated October 2026 from our full reviews · How we score
600 mg of NAC plus 25 mcg of selenium per capsule for about $0.44 a day; well made and plainly labeled, but NAC's benefits for healthy adults are modest.
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A hugely popular caffeinated amino drink: 100 mg natural caffeine plus a 5 g proprietary amino blend led by taurine, glutamine and arginine, so EAA doses are unknown.
We may earn a commission when you buy through these links — it never affects our scores. How we make money
We may earn a commission when you buy through these links — it never affects our scores. How we make money
The short answer
Choose NOW Foods if…
- Adults who want a plain, fully disclosed NAC at the commonly studied 1,200 mg daily dose
- Budget-minded shoppers comparing NAC brands
- People who prefer NAC from a manufacturer with accredited in-house labs
- You care most about value, transparency
Choose Optimum Nutrition if…
- A mild, flavored caffeine boost before training
- A sugar-free alternative to soda or energy drinks
- Athletes who want an Informed Choice certified energy mix
- You care most about quality & purity, experience
Key differences
- Biggest scoring gap
- Transparency: NOW Foods 8.0, Optimum Nutrition 5.0. This factor covers full label disclosure (no proprietary blends), available COAs, honest marketing.
- Independent testing
- Only Optimum Nutrition carries Informed Choice; NOW Foods has no independent certification we could verify. Informed Choice: monthly blind market-sample testing for banned substances.
- Formula
- Of the key ingredients in our reviews, only Optimum Nutrition lists caffeine and beta-alanine.
- Format
- NOW Foods: capsule, 100 servings per container; Optimum Nutrition: powder, 30 servings per container.
- Dietary labels
- Only NOW Foods is labeled gluten-free, dairy-free, soy-free and non-GMO. Only Optimum Nutrition is labeled sugar-free.
Side by side
| NAC 600 mg Capsules with Selenium | Essential AMIN.O. Energy | |
|---|---|---|
| Our score | 7.0 / 10 | 7.0 / 10 |
| Efficacy (30%) | 5.8 | 5.8 |
| Quality & Purity (25%) | 7.5 | 8.3 |
| Value (20%) | 7.6 | 6.8 |
| Experience (15%) | 7.4 | 8.5 |
| Transparency (10%) | 8.0 | 5.0 |
| Form | Capsule | Powder |
| Serving | 1 Capsule100 servings per container | 2 scoops (9 g)30 servings per container |
| Price per serving | $0.22 | See retailer |
| Testing & certifications | cGMP facilityKosherHalal | Informed Choice |
| Dietary | Gluten-free, Dairy-free, Soy-free, Non-GMO | Sugar-free |
| Key ingredients |
|
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| Flavors | — | 8 (Watermelon, Blue Raspberry, Concord Grape…) |
| Creator video reviews | 3 | 3 |
Pros and cons
NAC 600 mg Capsules with Selenium
- 600 mg of NAC per capsule, matching doses used in research when taken twice daily
- Simple, fully disclosed label: NAC plus 25 mcg of selenium and no proprietary blend
- NOW tests products in ISO 17025-accredited in-house labs and holds third-party GMP certification
- Evidence for noticeable benefits in healthy adults is limited
- Sulfur smell and capsule speckling are common, and some users report stomach upset
Essential AMIN.O. Energy
- 100 mg of caffeine per serving from green tea and coffee bean extracts
- Zero sugar and 14 flavors, with taste praised across thousands of reviews
- ON's support site lists it as Informed Choice certified
- Proprietary 5 g amino blend hides individual amino acid doses
- Blend is led by taurine, glutamine and arginine; tryptophan is not listed
Our verdict: NOW Foods vs Optimum Nutrition
NOW Foods and Optimum Nutrition are evenly matched overall (7.0 vs 7.0 out of 10), so the right pick depends on the differences above. Each full review shows the evidence, testing and buyer feedback behind these scores.