What the published trials measured
The human trials summarised below were short and involved small groups of volunteers, and the company that sells the ingredient funded or supported some of them. Each reference was checked against its PubMed record before being listed. The descriptions use the past tense because they report what happened in those studies, not what will happen for anyone else.
Blood arginine and silicon over six hours (2015)
Kalman and colleagues ran an open-label study in ten healthy men with an average age of about 27. Each man took Nitrosigine capsules daily for 14 days. On day 1 and again on day 14, the researchers took blood and saliva samples before that day's intake and at eight time points over the following six hours. They measured plasma arginine, serum silicon and salivary nitrite, which was used as an indirect marker of nitric oxide.
On day 1, plasma arginine was above its starting level from the first sample at 30 minutes, and the average peak came at about 1.1 hours. Serum silicon peaked later, at an average of about 2.4 hours, with wide variation between participants. After 14 days, plasma arginine four hours after intake was higher than at the same point on day 1. The change in salivary nitrite after the first intake was not statistically significant; by day 14, the resting value was higher in six of the ten men and unchanged in four. The authors recorded no adverse events.
The limits are considerable. There was no placebo or comparison group, everyone involved knew what was being taken, all ten volunteers were young men, and salivary nitrite is an indirect marker that the authors noted can be altered by oral bacteria, antiseptic mouthwash and antibiotics. Ten people are far too few to show how often uncommon unwanted effects occur. The paper reports no conflicts of interest and does not name a funder; the test product was Nitrosigine from Nutrition 21, LLC.
A resting blood vessel measurement (2020)
Rogers, Gills and Gray at the University of Arkansas compared a single serving of Nitrosigine, a single serving of citrulline malate and a dextrose placebo in 24 healthy, physically active young adults, 16 men and 8 women. The study was randomised and double-blind, and each participant completed all three conditions at least a week apart. The outcome was flow-mediated dilation of the brachial artery: an ultrasound measure of how much the main artery of the upper arm widens after a cuff on the forearm is released. It was taken at rest, before and 60 minutes after each serving.
The authors reported differences between the two active servings and placebo in this resting marker. The study recorded one resting marker on single days. It did not measure exercise, muscle size, endurance or performance, and a sample of 24 cannot show how often unwanted effects occur. It was funded by an Arkansas state undergraduate research fund and a University of Arkansas Honors College grant; the costs of publishing the paper were paid by an unrestricted grant from Nutrition 21, LLC, and the authors declared no competing interests.
Timed cognitive test scores (2016)
Kalman and colleagues also reported two double-blind, placebo-controlled crossover studies in healthy men aged 18 to 35. In the first, 11 men who trained with weights took Nitrosigine or placebo for 14 days in each period; in the second, 16 men who exercised less took it for 3 days in each period. Both used the Trail Making Test, a timed pen-and-paper task in which numbered and lettered circles are joined in order. The authors reported differences in part B completion times during the Nitrosigine periods; in the first study the comparison was made against each man's own starting score rather than against placebo.
Both studies were small, included only men and lasted no more than two weeks per period, and a single timed test is a narrow measure. The work was funded through a restricted grant from Nutrition 21, LLC, which also supplied the ingredient, and two of the four authors were employees of the company.
These summaries describe what the studies measured in their volunteers, and none of this is a claim about any product.
Regulatory position in the UK
In Great Britain, a health claim may only be made for a food, including a food supplement, if it is authorised and listed in the GB Nutrition and Health Claims Register. The EU keeps an equivalent register. Neither register lists an authorised health claim for arginine, arginine silicate, inositol-stabilised arginine silicate or glycerol. Claims proposed for arginine, including claims about blood vessel function and physical performance, were assessed by EFSA, the EU agency that gives scientific opinions on proposed claims, and none was authorised.
For that reason this page makes no claim about blood flow, pumps, endurance, focus or performance, and no such claim is made for any product that contains Nitrosigine. The studies above are reported for information only. Nitrosigine is an ingredient of food supplements for adults; it is not a medicine and it is not a research compound.
Where it appears in the Free Muscle range
In the Free Muscle range, Nitrosigine is an ingredient of NitraGlyc, which combines Nitrosigine with glycerol in a stimulant-free capsule, 60 capsules per pack. The amount of each ingredient per serving is as stated on the label. Every Free Muscle batch is assayed by Janoshik Analytical, an independent laboratory, and the certificate of analysis for a batch is available by email on request, quoting the batch number printed on the pack. See NitraGlyc, 60 capsules, or the pre-workout collection, which lists every pre-workout we stock.
Directions
NitraGlyc is a food supplement. Directions for use and the serving are stated on the label; follow them and do not exceed the stated serving. Neither Nitrosigine nor glycerol carries an authorised health claim in the UK or EU, so no performance claim is made for the product.
Common questions
Is Nitrosigine a stimulant?
No. Nitrosigine is a complex of arginine, silicate and inositol, and none of these is a stimulant in the way caffeine is. NitraGlyc contains no caffeine or other stimulant. That is a description of what is in the capsule, not a statement about how anyone will feel or train after taking it.
Is Nitrosigine a SARM or a research compound?
No. It is not a SARM, a peptide or a research chemical. It is a food ingredient, and NitraGlyc is a food supplement for adults, intended to be taken as directed on the label.
Does Nitrosigine have an authorised health claim?
No. There is no authorised health claim for Nitrosigine, for arginine or arginine silicate, or for glycerol, so no claim of any kind is made for NitraGlyc. The trials described above are reported as research findings, not as statements about the product.
How do I request the certificate of analysis for my batch?
Every Free Muscle batch is assayed by Janoshik Analytical, an independent laboratory. The certificate for your batch is available by email on request: quote the batch number printed on your pack. The lab tests page explains what a certificate of analysis shows.
Related reading: Nitrosigine vs citrulline malate in a 24-person vasodilation trial and what "stimulant-free pre-workout" means on a UK supplement label.
How do delivery and returns work?
UK delivery is free and tracked on every order. Orders placed before 2pm, Monday to Friday, are processed the same working day. Unopened products can be returned within 30 days. You must be 18 or over to order.
NitraGlyc is a food supplement for adults aged 18 and over, not a medicine. Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. Nothing on this page is medical advice, and the research summaries describe published studies rather than making claims about any product.
References
- Kalman DS, et al. A clinical evaluation to determine the safety, pharmacokinetics, and pharmacodynamics of an inositol-stabilized arginine silicate dietary supplement in healthy adult males. Clin Pharmacol. 2015;7:103-109. PMID: 26504409.
- Rogers JM, et al. Acute effects of Nitrosigine and citrulline malate on vasodilation in young adults. J Int Soc Sports Nutr. 2020;17(1):12. PMID: 32093766.
- Kalman D, et al. Randomized Prospective Double-Blind Studies to Evaluate the Cognitive Effects of Inositol-Stabilized Arginine Silicate in Healthy Physically Active Adults. Nutrients. 2016;8(11):736. PMID: 27869715.
