Stimulant-free pre-workout on a UK supplement label: what the term means

On a UK supplement label, stimulant-free pre-workout means a food supplement marketed for the period before training that contains no caffeine or other stimulants. It describes what is left out, not what the product does. This guide explains what that phrase does and does not tell you, what the NitraGlyc stimulant-free supplement lists on its product page, and how to judge any supplement label in the UK. It is a buyer's guide built on regulators and published studies, not a promise of results.

Key takeaways

• "Stimulant-free" describes what is left out. It says nothing on its own about whether the ingredients that remain have been shown to work.
• The NitraGlyc product page lists two ingredients, nitrosigine and glycerol, in a pack of 60 capsules, and states that every batch is assayed by Janoshik Analytical.
• The page does not give a per-ingredient amount in the text we reviewed, so this guide gives no intake figures. Follow the label and do not exceed the stated daily portion.
• No health claim is authorised in Great Britain for glycerol or for the other ingredient families we checked, so anything you read that promises a pump, performance or hydration benefit from a capsule deserves scepticism.
• The nitrosigine studies we cite were short and mostly small, and none of the studies we cite tested this capsule.
• If you have a medical condition, are pregnant or breastfeeding, or take medicines, speak to a doctor or pharmacist before using any supplement.

What is in the product

The product page describes NitraGlyc as a stimulant-free pre-workout food supplement in a 60-capsule pack. It names two ingredients: nitrosigine and glycerol. The page also states that it contains no caffeine and no other stimulants, and that each batch is assayed by Janoshik Analytical, with the batch number on the pack. Those are the only product facts this article relies on.

The page does not state how much nitrosigine or glycerol each capsule contains, nor a recommended daily portion in the text we reviewed. A figure such as "3 g per capsule" appears in the product description but is ambiguous: it does not say how that total divides between ingredients. For that reason, read the printed label on your pack for the real numbers and do not infer a dose from the web page.

Nitrosigine in plain English

Nitrosigine is a trade name for inositol-stabilised arginine silicate, often shortened to ASI. Arginine is an amino acid. Silicate here refers to a silicon-containing partner, and inositol is used to stabilise the complex. Arginine is described as a precursor of nitric oxide, which researchers study in relation to endothelial (blood vessel lining) function (Proctor et al., 2007).

Human research on ASI exists, but it is modest. In one single-group study (all ten took the active product, with no placebo arm described in the abstract), ten healthy men aged about 27 took an arginine silicate supplement for 14 days. Blood arginine rose within the first hour after dosing, and after 14 days a shift in baseline salivary nitrite reached statistical significance, while the change after the first dose did not. The authors reported no safety concerns within that specific protocol, in ten men, and said further study was warranted (Kalman et al., 2015). With ten people and no placebo group reported, that study speaks to absorption more than to any training outcome.

A randomised, double-blind crossover trial of 24 young adults measured flow-mediated dilation, an ultrasound test of how much an artery widens. An hour after a single dose of nitrosigine, the measure rose by 31% compared with a 2% fall after a dextrose placebo (Rogers et al., 2020). That is a laboratory vascular measurement at rest. It is not a measure of a training session, and the study did not test the NitraGlyc capsule.

Other human studies on ASI looked at thinking tests rather than exercise. In two double-blind crossover studies in healthy men, Trail Making Test B times improved against baseline after 14 days and, in a second study, against placebo over a short window (Kalman et al., 2016). In 19 young adults, one acute dose with dextrose improved the total score on a neuropsychological test battery (RBANS) and the immediate memory score against placebo, with no difference in other cognitive areas (Gills et al., 2021). These were short studies in healthy volunteers, none measured exercise performance, and the 2021 authors said more research is needed on other cognitive domains, in older populations and on long-term effects (Gills et al., 2021). A study on gamers used a related product that also contains inositol, so its results should not be read across to a different formulation (Tartar et al., 2019).

Glycerol in plain English

Glycerol is a naturally occurring three-carbon alcohol. It is the structural backbone of triacylglycerol molecules. In sports research it has been studied as a way to hold extra water in the body, an approach called hyperhydration (Robergs and Griffin, 1998).

That research is worth understanding, because it is often quoted loosely. The studies give glycerol as a solution measured by body weight and dissolved in a large volume of fluid, taken over about an hour, with the gap before exercise varying between studies (30 minutes in the guidelines review, about two and a half hours in a 2003 cycling trial). A guidelines review describes one such protocol (van Rosendal et al., 2010), and the cycling trial is Marino et al., 2003. Among the studies we reviewed, none tested a small capsule amount of glycerol without that fluid load. So the hyperhydration literature describes a drink protocol, not a capsule.

How to read a supplement label

Whichever stimulant-free pre-workout you are considering, the same checks apply. England's labelling rules (parallel rules apply in Scotland and Wales) require certain information on the pack, so a label that omits it is a warning sign.

Then read the front of the pack with a sceptical eye. Words such as "pump", "boost" or "performance" are marketing language unless an authorised claim stands behind them. Section UK food-supplement rules and health claims explains how to check.

Also check the ingredient list for "proprietary blends". Some labels list ingredients as a blend without separate amounts; regulation 6 requires the amount of the characterising substance per daily portion in numerical form, so check that it is shown. If amounts are not shown on the pack, ask the seller before you buy.

What authorities say about intake and cautions

We found no authority intake figure for NitraGlyc, for nitrosigine as a branded ingredient, or for a capsule of glycerol in this context, so this guide gives none. The practical instruction is simple: check the product label, follow the daily portion printed there, and do not exceed it.

The Food Standards Agency's food supplements guidance takes the same line. It advises buyers to follow the dose on the label and notes that taking more than the recommended dose can potentially lead to effects such as nausea and headaches. It also advises checking with a GP if you are pregnant, breastfeeding, have a medical condition or take prescribed medication, and stopping and contacting a healthcare professional if you feel unwell (FSA food supplements guidance).

Why research doses do not transfer to your capsule

It is tempting to look up the amounts used in studies and treat them as targets. That is a mistake for three reasons.

• Different products. A safety trial on free L-arginine used pharmaceutical-grade arginine hydrochloride in overweight or obese adults over 90 days (McNeal et al., 2018). That describes arginine, not nitrosigine, and not a capsule.
• Different delivery. Glycerol hyperhydration trials use a large fluid bolus, as covered above.
• Different people. Study participants, whether healthy volunteers, overweight adults or animals, took part under study conditions that differ from everyday use.

Glycerol reviews do mention possible effects. A sports-medicine review says side effects from glycerol ingestion are rare but include nausea, gastrointestinal discomfort and light-headedness (van Rosendal et al., 2010). A 1981 clinical review describes glycerol as a potent osmotic dehydrating agent, notes concern about hyperosmolality with rebound cerebral overhydration in clinical use, and says intravascular haemolysis does not occur with oral use but can with intravenous use (Frank et al., 1981). That review concerns hospital doses, not capsule supplements.

If you want to read about intake for a different supplement, our article on creatine and taurine evidence shows how authority-based figures are presented, always alongside the instruction to check the label.

Who should speak to a doctor first

The FSA advises speaking to a GP before using a supplement if you are pregnant or breastfeeding, have a medical condition, or take prescribed medication. That applies here. Some specific situations deserve extra thought.

• Anyone taking prescribed medicines. Ask a pharmacist. One arginine trial in overweight adults reported lower systolic blood pressure in women (McNeal et al., 2018).
• People with diabetes or blood-sugar concerns. The arginine research includes measures of glucose and insulin in animal and human studies, so ask before adding anything new. One rat study reported different insulin responses in males and females (Proctor et al., 2007), which is an animal finding, not a human one.
• People who are pregnant or breastfeeding. None of the human studies cited here tested these ingredients in pregnancy or breastfeeding. The FSA advises checking with a GP first.
• Under-18s. We found no cited study in under-18s, so there is no evidence here for that age group; speak to a doctor or pharmacist first.
• Anyone with a history of digestive upset. Glycerol reviews list nausea and gastrointestinal discomfort as possible effects.
• Tested athletes. Papers from 2012 and 2015 report that glycerol was on the World Anti-Doping Agency's prohibited list at that time (Polyviou et al., 2012; Savoie et al., 2015). We have not checked the current list and the status may have changed, so if you compete in a tested sport, check the current Prohibited List with your governing body.

Quality: third-party batch testing and certificates

A supplement label tells you what the seller says is inside. Third-party batch testing is how you check that claim. An independent laboratory analyses a sample from a specific production batch and issues a Certificate of Analysis, usually abbreviated to CoA, listing what was measured and what was found.

The NitraGlyc product page states that every batch is assayed by Janoshik Analytical, that the batch number is printed on the pack, and that the certificate is emailed on request. We present that as the brand's statement. We have not independently reviewed the laboratory's accreditation or methods in this article; our explainer on what Janoshik Analytical is covers the background.

To get the certificate for your pack, email the batch number printed on the label together with the product name. The process is described on the lab tests page.

What a useful certificate shows

Check that the certificate you receive shows:

• The product name and a batch number that matches your pack.
• Identity and purity results, which is the scope of the Janoshik assay as described on the product page.

Our guide on how to read a certificate of analysis walks through each section. A certificate confirms what was found in a sample. It does not show that a product has any effect, and it does not replace the label's own dose and warning information.

The FSA guidance also advises caution about counterfeit or unusually cheap products and unreputable online sellers. A batch number lets you ask for the certificate for the exact batch you hold.

UK food-supplement rules and health claims

In England a food supplement is legally a food whose purpose is to supplement the normal diet. It is a concentrated source of a vitamin, mineral or other substance with a nutritional or physiological effect, and it is sold in dose form such as capsules, tablets or sachets of powder (Food Supplements (England) Regulations 2003, regulation 2). The product page describes NitraGlyc as a food supplement. Scotland and Wales have parallel regulations, which we did not review for this article.

Food supplements are not medicines. The FSA guidance says food supplements should not be sold with claims to prevent or treat a medical condition, and that doing so is an offence (FSA food supplements guidance).

The claims register

Health claims are prohibited unless they are authorised and on the approved list. Any permitted claim must come with a statement about a varied, balanced diet and healthy lifestyle, information on the quantity and pattern of consumption needed, a statement for people who should avoid the food where relevant, and a warning if excess consumption may be a risk (Regulation 1924/2006, Article 10, as retained). Claims about the rate or amount of weight loss are banned outright (Article 12).

The Great Britain nutrition and health claims register lists every authorised and rejected claim, and only authorised claims may be used in Great Britain (GB NHC register). The version updated on 19 May 2026 is the one we checked.

We searched that register's health claims sheet for arginine, silicon, inositol, glycerol and nitric oxide. Every matching entry was marked non-authorised, and nitrosigine itself was not listed. The only authorised exercise-hydration claims relate to carbohydrate-electrolyte solutions with strict composition conditions, which do not describe a glycerol capsule. That was a keyword search, so a differently worded claim could in principle exist, but we found none.

The practical reading is straightforward. The NitraGlyc product page itself says no health claim is authorised for nitrosigine or glycerol and that none is made. Accordingly, this article does not say what the capsule does. Where we describe studies, we describe what happened in the named people or animals.

When you see a pre-workout advert, ask three questions:

1. Is the claim on the GB register as authorised?
2. Does the advert give the required statements about diet and quantity?
3. Does it promise a medical outcome, or refer to the rate or amount of weight loss? Those are not permitted. Any other health claim must be authorised on the register.

The FSA guidance says concerns can be reported to your local authority.

How to order from Free Muscle

NitraGlyc is listed on its NitraGlyc 60-capsule product page, and the other food supplement on the site, CREATREN, is in the performance nutrition collection. Free Muscle also sells research compounds and gym apparel; research compounds are sold for laboratory research use only to customers aged 18 or over, and they are not medicines or food supplements. Nothing on the site is medical advice.

• Delivery: UK delivery is free and tracked, in plain packaging. Standard UK delivery takes 2 to 5 working days. Orders placed before 2pm UK time, Monday to Friday, are processed the same working day. Details are on the shipping page.
• Returns: unopened items in their original packaging can be returned within 30 days; see the guarantee page. Apparel returns follow the refund policy.
• Certificate: once your pack arrives, email the batch number from the label with the product name to request the batch's Certificate of Analysis.

Frequently asked questions

What does stimulant-free pre-workout mean on a UK supplement label?

It means the product is sold without caffeine or other stimulants. It says nothing on its own about whether the remaining ingredients have any effect. In England the label must still carry the words "food supplement", the amount of the characterising substance per recommended daily portion, the portion itself with a warning not to exceed it, and a statement that supplements should not replace a varied diet. Check the product label, and speak to a doctor or pharmacist if you have a medical condition, are pregnant or breastfeeding, or take medicines.

What does stimulant-free pre-workout mean?

It means the product is sold without caffeine or other stimulants. For NitraGlyc, the product page states exactly that. It does not tell you whether the remaining ingredients have any effect, so read the label and the studies rather than the slogan.

What is nitrosigine?

Nitrosigine is the trade name for inositol-stabilised arginine silicate. The human studies we reviewed were short, mostly small, and covered absorption, a vascular measurement at rest and thinking tests, as described above (Kalman et al., 2015; Rogers et al., 2020).

Is a glycerol supplement the same as a glycerol hyperhydration drink?

No. The hyperhydration studies used glycerol in a large volume of fluid taken in a set routine before exercise (van Rosendal et al., 2010). We found no study testing a small capsule amount without that fluid load.

Does glycerol hyperhydration improve performance?

Evidence is mixed. A meta-analysis found glycerol held more fluid than water and reported a small endurance gain from only four studies, with the authors calling for more data (Goulet et al., 2007). Individual trials in warm conditions found no performance difference between glycerol and control drinks: seven moderately to well-trained people over a 60-minute self-paced cycling test (Marino et al., 2003), ten recreationally active people over a 5 km run (Jolicoeur Desroches et al., 2023), and 13 endurance runners over a half-marathon, where glycerol was combined with sodium chloride (Jardine et al., 2025). The latter two trials did find greater fluid retention with their glycerol protocols (in the 2025 trial, glycerol combined with sodium chloride). A review described the overall evidence as neither clearly for nor against a performance advantage (Nelson and Robergs, 2007).

Is there an authorised health claim for these ingredients?

Not that we found. A keyword search of the 19 May 2026 GB register returned only non-authorised entries for arginine, silicon, inositol and glycerol (GB NHC register).

Can I use a stimulant-free pre-workout instead of a varied diet?

No. Supplements are not a substitute for a varied diet, and England's labelling rules require that statement (parallel rules apply in Scotland and Wales).

Sources

1. Kalman DS, Feldman S, Samson A, Krieger DR. 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;7:103-9. DOI link PMID 26504409
2. Rogers JM, Gills J, Gray M. Acute effects of Nitrosigine and citrulline malate on vasodilation in young adults. J Int Soc Sports Nutr. 2020;17(1):12. DOI link PMID 32093766
3. Kalman D, Harvey PD, Perez Ojalvo S, Komorowski J. Randomized prospective double-blind studies to evaluate the cognitive effects of inositol-stabilized arginine silicate in healthy physically active adults. Nutrients. 2016;8(11). DOI link PMID 27869715
4. Gills JL, Campitelli A, Jones M, et al. Acute inositol-stabilized arginine silicate improves cognitive outcomes in healthy adults. Nutrients. 2021;13(12). DOI link PMID 34959823
5. Tartar JL, Kalman D, Hewlings S. A prospective study evaluating the effects of a nutritional supplement intervention on cognition, mood states, and mental performance in video gamers. Nutrients. 2019;11(10). DOI link PMID 31581523
6. Proctor SD, Kelly SE, Vine DF, Russell JC. Metabolic effects of a novel silicate inositol complex of the nitric oxide precursor arginine in the obese insulin-resistant JCR:LA-cp rat. Metabolism. 2007;56(10):1318-25. DOI link PMID 17884439
7. McNeal CJ, Meininger CJ, Wilborn CD, Tekwe CD, Wu G. Safety of dietary supplementation with arginine in adult humans. Amino Acids. 2018;50(9):1215-1229. DOI link PMID 29858688
8. Goulet ED, Aubertin-Leheudre M, Plante GE, Dionne IJ. A meta-analysis of the effects of glycerol-induced hyperhydration on fluid retention and endurance performance. Int J Sport Nutr Exerc Metab. 2007;17(4):391-410. DOI link PMID 17962713
9. van Rosendal SP, Osborne MA, Fassett RG, Coombes JS. Guidelines for glycerol use in hyperhydration and rehydration associated with exercise. Sports Med. 2010;40(2):113-29. DOI link PMID 20092365
10. Nelson JL, Robergs RA. Exploring the potential ergogenic effects of glycerol hyperhydration. Sports Med. 2007;37(11):981-1000. DOI link PMID 17953468
11. Marino FE, Kay D, Cannon J. Glycerol hyperhydration fails to improve endurance performance and thermoregulation in humans in a warm humid environment. Pflugers Arch. 2003;446(4):455-62. DOI link PMID 12695914
12. Jolicoeur Desroches A, Naulleau C, Deshayes TA, et al. Effect of glycerol-induced hyperhydration on a 5-kilometer running time-trial performance in the heat in recreationally active individuals. Nutrients. 2023;15(3). DOI link PMID 36771308
13. Jardine WT, Condo D, Aisbett B, et al. The addition of glycerol and sodium chloride to a hyperhydration protocol does not improve half-marathon time-trial performance in trained runners in warm conditions. Int J Sports Physiol Perform. 2025;20(6):770-778. DOI link PMID 40139199
14. Savoie FA, Dion T, Asselin A, Goulet ED. Sodium-induced hyperhydration decreases urine output and improves fluid balance compared with glycerol- and water-induced hyperhydration. Appl Physiol Nutr Metab. 2015;40(1):51-8. DOI link PMID 25494972
15. Polyviou TP, Easton C, Beis L, et al. Effects of glycerol and creatine hyperhydration on doping-relevant blood parameters. Nutrients. 2012;4(9):1171-86. DOI link PMID 23112907
16. Frank MS, Nahata MC, Hilty MD. Glycerol: a review of its pharmacology, pharmacokinetics, adverse reactions, and clinical use. Pharmacotherapy. 1981;1(2):147-60. DOI link PMID 6927604
17. Robergs RA, Griffin SE. Glycerol. Biochemistry, pharmacokinetics and clinical and practical applications. Sports Med. 1998;26(3):145-67. DOI link PMID 9802172
18. Food Standards Agency. Food supplements guidance. GOV.UK, published 25 June 2026.
19. Great Britain nutrition and health claims (NHC) register. GOV.UK, last updated 19 May 2026.
20. The Food Supplements (England) Regulations 2003, regulation 2 and regulation 6. legislation.gov.uk.
21. Regulation (EC) No 1924/2006 as retained, Article 10 and Article 12. legislation.gov.uk.