Transparent Labs BULK Black Pre-Workout Review 2026

L-Citrulline Malate (the citrulline salt of malic acid) is the most evidence-supported nitric oxide precursor in sports nutrition. Citrulline converts to arginine in the kidneys, which then drives nitric oxide synthase (NOS) to produce NO — a vasodilator that widens blood vessels and increases blood flow to working muscles. Unlike L-arginine supplementation (which is poorly absorbed orally), citrulline malate reliably raises plasma arginine and NO levels because it bypasses first-pass liver metabolism. The 2:1 ratio means approximately 5,300mg of actual citrulline per 8,000mg dose — comfortably above the 3,000–6,000mg threshold validated in RCTs for pump, endurance, and lactate clearance effects. A landmark study (Pérez-Guisado & Jakeman, 2010) demonstrated 8g of citrulline malate significantly reduced muscle soreness and increased repetitions to failure vs placebo in a bench press protocol. This is that exact dose.

Beta-alanine is a beta-amino acid that combines with L-histidine to form carnosine in skeletal muscle. Carnosine buffers the hydrogen ions (H+) produced during high-intensity exercise — the ions responsible for the "burn" and the drop in force production during near-failure sets. Supplementing with beta-alanine chronically (4–6 weeks) saturates muscle carnosine stores, extending the time before acid-mediated fatigue limits performance. A 2012 meta-analysis in Amino Acids (Hobson et al.) analysing 15 studies confirmed statistically significant improvements in exercise capacity at doses of 3.2g/day or more. At 4,000mg per serving, BULK Black exceeds the minimum clinical threshold and matches the upper efficacy range for acute dosing. The paresthesia (skin tingling, particularly on face, ears, and forearms) that many users experience is a harmless pharmacological effect from beta-alanine's interaction with sensory receptors — not an allergic reaction or sign of toxicity. Full beta-alanine guide →

Betaine (trimethylglycine or TMG) is a naturally occurring compound found in sugar beets that serves as an osmolyte — helping cells retain water and maintain volume under osmotic stress. This cellular hydration effect is important for maintaining muscle performance during training. Multiple studies have shown betaine supplementation at 2,500mg/day improves power output, work capacity, and body composition. A 2011 study in the Journal of Strength & Conditioning Research (Trepanowski et al.) demonstrated significant improvements in bench press and squat performance with chronic betaine supplementation. BetaPure® is the pharmaceutical-grade form with standardised purity — not generic betaine anhydrous, which can have variable quality and bioavailability. The exact 2,500mg dose here matches the most consistently replicated human trial dosing.

Alpha-GPC (Alpha-Glyceryl Phosphoryl Choline) is the most bioavailable oral choline source available. Choline is an essential precursor to acetylcholine — the primary neurotransmitter mediating neuromuscular junction signalling. In the gym context, higher acetylcholine availability enhances the mind-muscle connection, sharpens focus, and improves motor unit recruitment. A 2008 study (Ziegenfuss et al.) demonstrated Alpha-GPC supplementation at 600mg acutely increased growth hormone secretion and produced meaningful improvements in peak power output in trained athletes. AlphaSize® is the trademarked, standardised form — 50% active alpha-GPC by weight, meaning 300mg of AlphaSize delivers 150mg of actual alpha-GPC. This is the most common effective dose in acute performance studies. The nootropic and focus effects are among the most consistently reported user experiences with BULK Black.

BULK Black uses a dual-caffeine strategy: 275mg of standard caffeine anhydrous (fast-acting, rapid CNS stimulation) plus 30mg of Infinergy® DiCaffeine Malate — a buffered form of caffeine bonded to malic acid that releases more slowly in the gut, extending the energy duration and reducing the drop-off that follows a caffeine anhydrous peak. The combined 305mg total caffeine places BULK Black in the high-stim category — equivalent to approximately 3.5 strong espresso shots. At 3–6mg/kg, this is appropriate for athletes weighing 50–100kg. For context: the EFSA identifies 400mg/day as the safe upper limit for healthy adults; one scoop of BULK Black uses ~75% of this daily limit. The L-Theanine at 200mg is critically important here — it modulates caffeine's effects by reducing the jitteriness and anxiety that can accompany high-dose caffeine without blunting the alertness or energy benefits. The caffeine-theanine combination is the most well-replicated cognitive enhancement stack in the literature. Full caffeine science guide →

L-Tyrosine is a conditionally essential amino acid that serves as the biosynthetic precursor to dopamine, norepinephrine, and epinephrine. During intense exercise, catecholamine neurotransmitters are depleted — contributing to both central fatigue (reduced drive) and peripheral fatigue. Tyrosine supplementation replenishes this precursor pool, helping maintain neurotransmitter synthesis during training stress. Research demonstrates tyrosine is particularly effective under conditions of stress, sleep deprivation, and cognitive demand — precisely the context of a hard training session. At 1,000mg, BULK Black is at the lower-to-mid end of the evidence-based range (500–2,000mg) but delivers meaningful support. The synergy with Alpha-GPC — which increases acetylcholine via the cholinergic pathway while tyrosine supports the catecholaminergic pathway — creates complementary nootropic coverage across multiple neurotransmitter systems.

Astragin® is a patented extract of Astragalus membranaceus and Panax notoginseng that upregulates intestinal transport proteins (particularly mTOR-regulated tight junction proteins) to improve nutrient absorption across the gut wall. The mechanism is well-documented: Astragin increases the expression of transporters that citrulline, arginine, amino acids, and other actives use to cross the intestinal epithelium. At 50mg — the exact clinical dose — it meaningfully improves the bioavailability of the entire BULK Black formula. Its inclusion represents a level of formulation sophistication absent from most competitors: not just adding ingredients, but ensuring those ingredients are actually absorbed effectively.

Boron (3mg) inhibits sex hormone-binding globulin (SHBG) — the protein that binds and inactivates free testosterone. By reducing SHBG, boron increases free testosterone availability. A 2011 study demonstrated 10mg/day boron produced significant increases in free testosterone over 7 days — at 3mg, the effect is smaller but meaningful when consistent. Vitamin D3 at 75mcg (3,000 IU) supports testosterone production through the androgen receptor pathway; low vitamin D status is strongly associated with reduced testosterone in men across multiple studies. For an athlete already supplementing vitamin D, this adds to the daily total; for those who are vitamin D-deficient (common in indoor athletes and those in low-sun climates), this is a meaningful performance-relevant addition.