NOW L-Arginine 1,000 mg Review: What the Tablet, the Dose, and the Research Say

Arginine was the original pump ingredient. Before citrulline took over the pre-workout aisle, arginine was the amino acid that supplement companies pointed to when they wanted to explain nitric oxide, and you can still find it in the formulas of products that have not changed their labels in a decade. It is also one of the cheapest supplements in the store, which makes it a good test of a simple question: when something is both cheap and widely sold, is it worth taking?

This article covers what is on the label, what the research says about oral arginine, how the label's directions compare with the doses that were studied, and what it costs to reach those doses.

What You Are Buying

The details below come from the Amazon listing for the NOW Supplements L-Arginine 1,000 mg, 120 tablets (ASIN B0013OVX3U), including the supplement panel shown in the listing's product images. The current listed price is $17.04. The listing also offers a two-pack and a 300-count option.

A few things stand out. The label is clean: one active, a short list of tablet excipients, and no proprietary blend. The directions are for two grams a day, taken as one tablet in the morning and one at night, and they say "as needed," which is a vague instruction for a supplement that has no established need in healthy people. The listing's feature bullet describes arginine as a nitric oxide precursor that "plays an important role in the dilation of blood vessels," which is true of the body's chemistry and does not mean a tablet will change your blood vessels. And the manufacturer's quality claim is about its facility, which we return to in the quality section.

What Arginine Is and Why People Take It

Arginine is an amino acid that your body makes and also gets from food. It is a building block of protein, it takes part in the urea cycle that clears ammonia, and it is the substrate that nitric oxide synthase converts into nitric oxide, the signaling molecule that relaxes blood vessel walls. That last fact is the entire pitch for the supplement. More arginine, the reasoning goes, should mean more nitric oxide, wider blood vessels, more blood flow to muscle, and better performance. Each step in that chain is a plausible biological idea. Whether it works when you swallow a tablet is a separate question that the research has had to answer directly.

It helps to keep two claims apart, because supplement marketing blurs them. The first is that arginine is important to your biology, which is true. The second is that swallowing extra arginine improves a healthy person's performance, which is the claim that needs evidence. Your body does not run short of arginine because you skipped a supplement. Dietary protein supplies it, and the body also makes it from citrulline in the kidneys. A lifter eating enough protein is already getting arginine every day. For background on how protein intake works, see our protein per day guide.

The Absorption Problem

The standard objection to oral arginine is that much of it never reaches the circulation. Schwedhelm and colleagues (2008) described oral arginine treatment as hampered by extensive presystemic elimination due to intestinal arginase activity, meaning enzymes in the gut wall break arginine down before it can be absorbed intact. In that double-blind, randomized, placebo-controlled crossover study of 20 healthy volunteers, six dosing regimens of placebo, citrulline, and arginine were compared after one week of oral supplementation. Citrulline dose-dependently increased the peak and total exposure of plasma arginine more effectively than arginine itself (P < 0.01). At the highest citrulline dose, 3 g twice daily, the arginine-to-ADMA ratio rose from 186 to 278, and urinary nitrate and cGMP, which are markers of nitric oxide signaling, increased. No treatment improved flow-mediated vasodilation over baseline.

Read that last sentence again, because it matters for a product like this one. In a carefully controlled pharmacology study, none of the regimens, including the arginine ones, improved the direct measure of how well arteries dilate. The study did find that when all the data were pooled, the rise in the arginine-to-ADMA ratio correlated with improved dilation, so the pathway is real. But the headline for a lifter is that citrulline is the better way to raise blood arginine, and the supplement under review is the less effective route. We cover that comparison in our L-citrulline guide, and the product we reviewed on the citrulline side is our Nutricost review.

What the Performance Research Shows

The performance literature on arginine is small and mixed. Alvares and colleagues (2011) reviewed it in Sports Medicine and found only five acute studies that evaluated exercise performance after arginine supplementation, three of which reported significant improvements. They found eight studies on chronic effects, four of which reported enhancements and four of which showed no change. The authors noted that whether any improvements were linked to increased nitric oxide production had yet to be demonstrated, that low oral doses of up to 20 g were well tolerated with rare side effects, and they concluded that it was premature to recommend arginine-containing supplements as an ergogenic aid for healthy, physically active people. That is a careful, conservative sentence from the people who reviewed the field.

The strongest recent direct test we found was a double-blind, placebo-controlled crossover study by Meirelles and Matsuura (2018). Twelve trained men received 6 g of arginine or placebo 60 minutes before a strength test of three sets to failure at 70 percent of one-rep max on the bench press and 80 percent on knee extensions, with two minutes of rest between sets. Plasma nitrite, a marker of nitric oxide, did not change after arginine or placebo. Repetitions fell from the first to the third set in both conditions, and there were no significant differences between arginine and placebo. The authors concluded that the results did not support using arginine as an ergogenic aid for strength performance in the context of acute use immediately before resistance exercise.

That is a small study, and a single small study should not carry much weight. What it adds is a specific, tested scenario that matches how most lifters would use this product: a few grams, about an hour before training, and measured outcomes that are exactly the ones the supplement claims to improve. It did not work. The most that can be said for the performance case is that the evidence is mixed, with some studies positive, and no one has shown a reliable effect for a healthy trained lifter. Our supplements blacklist includes oral arginine in its pump-aisle section for the same reason, and our ingredient evidence ranking shows where citrulline sits by comparison.

Blood Pressure: The Evidence That Is Real

If there is a case for oral arginine, it is on blood pressure, and the meta-analyses are consistent. Dong and colleagues (2011) pooled 11 randomized, double-blind, placebo-controlled trials involving 387 participants, with arginine given at 4 to 24 g per day. Compared with placebo, arginine lowered systolic blood pressure by 5.39 mm Hg (95 percent CI -8.54 to -2.25, P = .001) and diastolic blood pressure by 2.66 mm Hg (95 percent CI -3.77 to -1.54, P < .001). Restricting the analysis to trials lasting four weeks or longer and to participants not taking antihypertensive medication gave similar results.

An updated dose-response meta-analysis by Shiraseb and colleagues (2022) pooled 22 randomized trials with 30 effect sizes and found a systolic drop of 6.40 mm Hg (95 percent CI -8.74 to -4.05) and a diastolic drop of 2.64 mm Hg (95 percent CI -3.94 to -1.40). The reductions appeared whether participants were normotensive or hypertensive, healthy or unhealthy. Two details are worth noting. The dose-response analysis put the effective dose for systolic pressure at 4 g per day or more, and no significant change was seen at doses above 9 g per day or in trials longer than 24 days or in obese participants, which means the relationship is not a simple "more is better." A 2026 meta-analysis (Shi and colleagues) of five trials with 202 participants, using ambulatory 24-hour monitoring, reported reductions of 4.23 mm Hg systolic and 3.04 mm Hg diastolic over 24 hours, and the authors cautioned that the number of studies was limited.

So for blood pressure the evidence is better than for performance. It is also not a reason for a healthy lifter to take arginine, because a few mm Hg in a person with normal pressure is not a goal, and for a person with elevated pressure the right move is a conversation with a physician, not a self-selected supplement. It is, however, the reason the safety section below talks about medication.

The Dose Problem: Two Tablets vs. the Studies

The label's directions are one tablet twice daily, which is 2 g a day. The blood pressure research used much more. This is the central mismatch of the product, and it is worth setting out as a table.

Three conclusions follow. At the label dose of 2 g per day, you are below the 4 g per day threshold that the dose-response analysis associated with a blood pressure effect, so the data we cite do not tell you what 2 g does. If you wanted to match the studied doses for blood pressure, you would be taking four to nine tablets a day, which is not what the label says and which we are not recommending. And for performance, the one acute trial we found used 6 g and found nothing, so even tripling the label dose is not supported by that evidence. In short, the label directions land in a dose range that has not been shown to do much of anything in the research we reviewed, and the doses that have been shown to lower blood pressure are two to four times higher.

What It Costs Per Day at Each Dose

At $17.04 for 120 tablets, each tablet costs about 14 cents, or about 14 cents per gram of arginine.

The label dose is cheap. The studied doses are not outrageous, but they are not trivial either, and the 9 g figure costs more than a dollar a day for an ingredient whose performance case is unproven. To put a reference point next to it, our Nutricost citrulline review calculated about 15 cents per 3 g scoop of L-citrulline at its listed price, which is a single scoop for roughly the same money as one arginine tablet. Prices fluctuate.

Safety, Tolerability, and Interactions

Arginine has a reasonably clean safety record at the doses in the label. Alvares and colleagues (2011) reported that low oral doses of up to 20 g are well tolerated and clinical side effects are rare in healthy subjects. Shao and Hathcock (2008), in a formal risk assessment of taurine, glutamine, and arginine, found no systematic pattern of adverse effects in human trials that would allow a standard upper limit to be set, and used an "observed safe level" approach instead. They identified 20 g per day of arginine as the level supported by strong evidence of no adverse effects in normal healthy adults, while noting that much higher doses had been tested without problems but that data above 20 g were not sufficient for a confident conclusion about long-term safety.

We went looking for a cited rate of stomach upset on oral arginine, since GI complaints are the side effect people most commonly mention, and did not find a trial we could verify and quote. We are therefore not going to put a number on it. The NOW label's instruction to take the tablet with at least 8 oz of water or juice is the manufacturer's own handling of the problem. If you try it, take it with food or a full glass of water and start with one tablet. A tablet that dissolves slowly in a dry stomach is the kind of thing that annoys people, and that is a practical observation and not a finding.

Quality and Third-Party Testing

The listing says NOW's manufacturing carries an "NPA A-rated GMP certification," which it describes as an examination of every aspect of the manufacturing process, including laboratory and testing methods for stability, potency, and product formulation. The label itself says the product was made and quality tested in the USA with globally sourced ingredients, in a GMP facility that processes other allergens. Those are facility-level and process-level claims. They are meaningful signals about manufacturing practice, but they are not the same as a product-level certification such as an independent program that tests individual lots for contaminants and banned substances. The listing does not state that this specific product carries such a certification. If you compete in a tested sport, check the bottle and the manufacturer's site, and ask for a certificate of analysis for your lot.

For a single-ingredient amino acid, the purity question is relatively simple: you want to know that each tablet contains the 1,000 mg it says and nothing unwanted. The label's description of the arginine as pharmaceutical grade is a manufacturer claim we cannot verify.

Arginine vs. Citrulline: The Comparison Logic

The question most lifters actually have is whether to buy arginine or citrulline. The logic is short. Both are marketed on the same nitric oxide story. Arginine is the direct precursor but is cleared in the gut, and in the head-to-head pharmacology study citrulline raised blood arginine more effectively. For performance, a meta-analysis of citrulline trials (Trexler and colleagues, 2019, 12 studies, 198 participants) found a small but statistically significant pooled benefit, with a Hedges' g of 0.20 (95 percent CI 0.01 to 0.39), while the arginine reviews we cite found mixed results and a recommendation that it was premature to endorse. For blood pressure, both have supportive meta-analyses, and the citrulline analysis pooled eight trials at 3 to 9 g per day and found a 4.10 mm Hg systolic drop. On price, a gram of arginine in this bottle costs about 14 cents, and a 3 g scoop of the citrulline we reviewed cost about 15 cents.

That does not make citrulline a miracle, and our review of it is equally cautious about the size of the effect. It means that if you are going to spend money on a nitric oxide ingredient for training, the evidence favors the other one. Arginine does not need to be bought at all for a lifter with a normal diet and normal blood pressure.

Who Should Buy It and Who Should Skip It

It might make sense if you are curious about arginine, you want a cheap, clean, single-ingredient tablet, you understand that the label dose is lower than the studied doses, and you have no medical reason to avoid it. As a product, it is well made and fairly priced, and it does exactly what it says: it delivers 1 g of arginine per tablet.

Skip it if your goal is a better pump or performance. The research does not support oral arginine for that, and the only acute strength trial we found at 6 g showed no effect. Skip it if you are taking blood-pressure medication, nitrates, or PDE5 inhibitors without medical guidance. And skip it if you are already taking citrulline or a pre-workout that contains it, since the two target the same pathway and citrulline is the better-supported choice.

The hierarchy is the same as always. Training, protein, sleep, and creatine will do far more for you, and our creatine monohydrate guide covers the one sports supplement with deep evidence behind it.

What Buyers Report

Buyers of the 1,000 mg tablets, rated about 4.7 out of 5 across tens of thousands of ratings on a supplement retailer's page, mostly talk about tablet size, taste and packaging.

• Tablet size: Opinions are split. Many say the tablets are easy to swallow, while a noticeable number call them large, with one saying the uncoated tablet was hard to get down.
• Taste: Most say there is little to no taste, though one dislikes the taste.
• Packaging and value: Buyers like the bottle, the tablet count, the fresh expiration dates, and fast shipping.
• Complaints: Besides size, a few report stomach discomfort or no noticeable difference.

Takeaway: buyers see a plain, well-packaged tablet whose main drawback is size. Buyer reports are anecdotal and are not the same as the research above; they are not evidence about what a supplement does and not advice.

How HonestLifter Is Reviewing This Product

HonestLifter's editorial model is longitudinal. A one-time first-impressions post tells you very little about a supplement, so the plan for each product is a written research review at the start, followed by dated checkpoint updates at 30 days, 60 days, 90 days, 6 months, and 12 months of use. The checkpoint updates are meant to report real use, real notes, and, where available, real data exports, not recycled research. You can read more in our longitudinal review program article.

This is a research review built on the label and published studies, and our own notes will be added as dated updates at the checkpoints below.

Checkpoint Update: 30-Day, 60-Day, 90-Day and 6-Month Notes (October 2026)

HonestLifter's owner reports the following from regular use. These are personal notes, not measurements.

• Use: Daily in the morning before training, taken with other morning supplements and washed down with the pre-workout drink.
• Effect: Nothing noticed, good or bad, that can be attributed to it. Because several supplements are taken together, one product's effect would be hard to isolate.
• Verdict: Would buy again.

Several supplements are taken together, so none of these notes isolates the effect of this product. The 12-month update will be added when it is written.

The Bottom Line

NOW L-Arginine 1,000 mg is a well-labeled, fairly priced version of an ingredient whose best days as a pump supplement are behind it. The tablet delivers what it promises. The research on oral arginine for performance is mixed and does not support recommending it to healthy lifters, the one acute trial we found at 6 g showed nothing, and oral arginine faces a real absorption handicap compared with citrulline. The blood pressure effect is more consistent in the meta-analyses, but those results come from 4 g a day or more, which is double the label's directions, and blood pressure is a medical topic and not a training goal.

Buy it only if you have a specific reason and understand the dose gap. Skip it if you want a pump, and consider citrulline instead. Talk to your doctor if you take blood-pressure medication.

References

1. Schwedhelm, E., Maas, R., Freese, R., Jung, D., Lukacs, Z., Jambrecina, A., Spickler, W., Schulze, F., & Boger, R.H. (2008). Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. British Journal of Clinical Pharmacology, 65(1), 51-59. doi:10.1111/j.1365-2125.2007.02990.x. PMID 17662090.
2. Alvares, T.S., Meirelles, C.M., Bhambhani, Y.N., Paschoalin, V.M., & Gomes, P.S. (2011). L-Arginine as a potential ergogenic aid in healthy subjects. Sports Medicine, 41(3), 233-248. doi:10.2165/11538590-000000000-00000. PMID 21395365.
3. Meirelles, C.M., & Matsuura, C. (2018). Acute supplementation of L-arginine affects neither strength performance nor nitric oxide production. Journal of Sports Medicine and Physical Fitness, 58(3), 216-220. doi:10.23736/S0022-4707.16.06680-9. PMID 27623757.
4. Dong, J.Y., Qin, L.Q., Zhang, Z., Zhao, Y., Wang, J., Arigoni, F., et al. (2011). Effect of oral L-arginine supplementation on blood pressure: a meta-analysis of randomized, double-blind, placebo-controlled trials. American Heart Journal, 162(6), 959-965. doi:10.1016/j.ahj.2011.09.012. PMID 22137067.
5. Shiraseb, F., Asbaghi, O., Bagheri, R., Wong, A., Figueroa, A., & Mirzaei, K. (2022). Effect of L-arginine supplementation on blood pressure in adults: a systematic review and dose-response meta-analysis of randomized clinical trials. Advances in Nutrition, 13(4), 1226-1242. doi:10.1093/advances/nmab155. PMID 34967840.
6. Shi, Y., Liu, Y., Zhou, Z., Xu, S., & Luo, P. (2026). Reassessment of the effect of oral L-arginine on blood pressure: a systematic review and meta-analysis based on ambulatory blood pressure monitoring. Nitric Oxide, 164, 60-68. doi:10.1016/j.niox.2026.07.004. PMID 42520885.
7. Shao, A., & Hathcock, J.N. (2008). Risk assessment for the amino acids taurine, L-glutamine and L-arginine. Regulatory Toxicology and Pharmacology, 50(3), 376-399. doi:10.1016/j.yrtph.2008.01.004. PMID 18325648.
8. Trexler, E.T., Persky, A.M., Ryan, E.D., Schwartz, T.A., Stoner, L., & Smith-Ryan, A.E. (2019). Acute effects of citrulline supplementation on high-intensity strength and power performance: a systematic review and meta-analysis. Sports Medicine, 49(5), 707-718. doi:10.1007/s40279-019-01091-z. PMID 30895562.
9. Barkhidarian, B., Khorshidi, M., Shab-Bidar, S., & Hashemi, B. (2019). Effects of L-citrulline supplementation on blood pressure: a systematic review and meta-analysis. Avicenna Journal of Phytomedicine, 9(1), 10-20. PMID 30788274.

Product details were taken from the Amazon listing for NOW L-Arginine 1,000 mg (120 tablets) and may change. HonestLifter carries no affiliate links. This article is educational and is not medical advice.