Underground Labs SCYTHE PWO 465 g

L-citrulline and citrulline malate

L-citrulline is an amino acid that the body converts to arginine, a precursor of nitric oxide, which widens blood vessels. Citrulline malate combines citrulline with malic acid².

Beta-alanine

Beta-alanine is an amino acid that combines with histidine in muscle to form carnosine, which helps buffer acid during intense exercise³.

Betaine (trimethylglycine)

Betaine (trimethylglycine) occurs naturally in beetroot, spinach and wheat. It acts as an osmolyte and as a methyl donor in homocysteine metabolism.

L-tyrosine

L-tyrosine is an amino acid that the body uses to make the neurotransmitters dopamine and noradrenaline. It is found in protein-rich foods; N-acetyl-L-tyrosine is a related form⁴.

Caffeine

Caffeine is a stimulant that blocks adenosine receptors in the brain, reducing perceived effort and fatigue. It is found in coffee, tea and energy drinks and is a common ingredient in pre-workout products⁵.

Dicaffeine malate (sold as Infinergy®) is caffeine bonded to malic acid. Its caffeine adds to the total caffeine in a product, but labels do not always state the caffeine equivalent.

Phenylethylamine (PEA) and Eria jarensis

β-Phenylethylamine (PEA) is a naturally occurring trace amine with stimulant properties. "Eria jarensis" extract is marketed as a source of related phenethylamines such as N-phenethyldimethylamine. These compounds belong to a large chemical family that also includes synthetic stimulants found in supplements⁶.

DMHA (2-aminoisoheptane, octodrine) and DMBA

DMHA, also labelled 2-aminoisoheptane or octodrine (2-amino-6-methylheptane), is a synthetic aliphatic amine stimulant found in pre-workout and weight-loss supplements, sometimes alongside the related compound DMBA⁷.

Yohimbine (yohimbe bark, rauwolscine)

Yohimbine is an alkaloid from the bark of the African tree Pausinystalia yohimbe. It blocks α2-adrenergic receptors, which increases noradrenaline release. Rauwolscine (alpha-yohimbine) is a closely related alkaloid.

L-citrulline and citrulline malate

A review of human studies found that citrulline supplementation raises plasma arginine, and that several studies report improved exercise performance or recovery, but the results are inconsistent².

Beta-alanine

The International Society of Sports Nutrition concludes that 4–6 g a day for at least 2–4 weeks raises muscle carnosine and improves performance in exercise lasting about 1–4 minutes³.

A meta-analysis found a significant overall ergogenic effect, with the size of the benefit depending on the type and duration of exercise⁸.

Betaine (trimethylglycine)

A meta-analysis found that betaine supplementation for at least 7 days improved muscular strength, especially lower-body strength, and may improve jumping performance⁹. The EU authorises a claim that betaine contributes to normal homocysteine metabolism at 1.5 g a day¹⁰.

L-tyrosine

A review found that tyrosine may support cognitive performance in short-term stressful or cognitively demanding situations, when these neurotransmitters are temporarily depleted, but found no consistent effect on physical exercise performance⁴.

Caffeine

The International Society of Sports Nutrition concludes that caffeine consistently improves exercise performance when consumed in doses of about 3–6 mg per kg of body mass, with benefits for muscular endurance, movement velocity, strength, sprinting, jumping and aerobic exercise⁵.

Phenylethylamine (PEA) and Eria jarensis

There are no controlled human trials showing that PEA or Eria jarensis extracts improve exercise performance or focus. Most published research concerns detection of phenethylamines in supplements and their regulatory status⁶¹¹.

DMHA (2-aminoisoheptane, octodrine) and DMBA

There are no controlled human trials showing that DMHA improves exercise performance or weight loss.

Yohimbine (yohimbe bark, rauwolscine)

A small trial in professional soccer players found reduced body fat with yohimbine but no change in body mass, muscle mass or performance¹². Larger, independent trials are lacking.

L-citrulline and citrulline malate

Studies differ in dose, form (citrulline or citrulline malate, often with an unverified ratio) and exercise test, and many are small. The mechanism behind any performance effect is not established².

Beta-alanine

Effects on strength and on endurance exercise beyond about 25 minutes are not established³. A single serving taken before training does not reproduce the daily supplementation used in research.

Betaine (trimethylglycine)

The studies are small and differ in dose and duration⁹.

L-tyrosine

Most studies are small and use single doses in laboratory settings⁴.

Caffeine

Responses vary widely between people, partly because of genetics and habitual caffeine use. Many studies use pure caffeine, so results do not automatically apply to multi-ingredient products⁵.

Phenylethylamine (PEA) and Eria jarensis

Product labels for phenethylamine ingredients are often unreliable. Supplements labelled as containing Eria jarensis that were tested were inaccurately labelled and contained high quantities of caffeine and undeclared stimulants¹³⁶.

DMHA (2-aminoisoheptane, octodrine) and DMBA

The research concerns detection of these stimulants in supplements, not their effects. Analyses of sports and weight-loss supplements have repeatedly found stimulants that were not declared, or quantities different from the label⁷¹¹.

Yohimbine (yohimbe bark, rauwolscine)

Evidence for fat loss or performance is limited to small studies. Supplement labels are often inaccurate: of 49 US yohimbine supplements tested, only 2 gave accurate information on both the quantity and the known adverse effects¹⁴.

L-citrulline and citrulline malate

Citrulline is generally well tolerated in the doses studied. Digestive discomfort has been reported, and people taking blood-pressure or erectile-dysfunction medication should ask a doctor, because citrulline raises arginine and nitric oxide production².

Beta-alanine

The only commonly reported side effect is paraesthesia, a harmless tingling of the skin that is more likely with larger single doses³.

Betaine (trimethylglycine)

Betaine is generally well tolerated; high intakes may raise blood cholesterol in some people.

L-tyrosine

People taking MAO inhibitors or thyroid medication should not use tyrosine supplements without medical advice.

Caffeine

EFSA concluded that single doses of up to 200 mg, and daily intakes of up to 400 mg from all sources, do not raise safety concerns for healthy adults. For pregnant and breastfeeding women, daily intakes up to 200 mg do not raise concerns for the foetus or infant¹.

Higher intakes can cause anxiety, sleep disturbance, raised heart rate and blood pressure, and digestive upset. Combining several caffeine sources (coffee, energy drinks, pre-workouts) raises total intake¹⁵.

Phenylethylamine (PEA) and Eria jarensis

Stimulants of this family can raise heart rate and blood pressure. A case report linked a supplement containing the related compound β-methylphenylethylamine to a haemorrhagic stroke during exercise¹⁵. Avoid combining with other stimulants, MAO inhibitors or antidepressants.

DMHA (2-aminoisoheptane, octodrine) and DMBA

Human safety data are lacking. As a sympathomimetic amine, DMHA may raise heart rate and blood pressure; avoid combining it with other stimulants. Contaminated supplements have caused positive doping tests¹¹.

Yohimbine (yohimbe bark, rauwolscine)

A review of poison-centre cases found that adverse events with yohimbine products had more serious outcomes than average exposures, including rapid heart rate, anxiety, high blood pressure and agitation¹⁶. People with heart conditions, high blood pressure, anxiety disorders or taking antidepressants should not use yohimbine.

Contains DMHA/DMBA, a synthetic stimulant that is not authorised as a novel food in the EU. Contains yohimbine. Isolated yohimbine is classified as a medicinal substance in several EU member states; its legal status depends on the country of sale.

L-citrulline and citrulline malate

L-citrulline is used in EU food supplements under national rules. No health claim for citrulline is authorised in the EU¹⁰.

Beta-alanine

Beta-alanine is used in EU food supplements under national rules. No health claim is authorised¹⁰.

Betaine (trimethylglycine)

Betaine is used in EU food supplements; the homocysteine claim may be used only in its authorised wording and conditions¹⁰.

L-tyrosine

Amino acids such as L-tyrosine are used in EU food supplements under national rules. No health claim is authorised¹⁰.

Caffeine

Caffeine is permitted in EU foods and food supplements, subject to labelling rules. It is not on the World Anti-Doping Agency Prohibited List¹⁷.

Phenylethylamine (PEA) and Eria jarensis

Phenethylamine stimulants are not authorised EU food supplement ingredients, and several related compounds are on the World Anti-Doping Agency Prohibited List as stimulants¹⁷¹⁸.

DMHA (2-aminoisoheptane, octodrine) and DMBA

DMHA and DMBA are not authorised as novel foods in the EU¹⁸. Octodrine and related stimulants are prohibited in competition by the World Anti-Doping Agency¹¹¹⁷.

Yohimbine (yohimbe bark, rauwolscine)

Yohimbine is a pharmacologically active substance. Its use in food is regulated under Regulation (EC) No 1925/2006 and national rules¹⁹, and several EU Member States treat it as a medicinal substance²⁰.