Buy Bulk Mass SARMs Stack UK | 4-in-1 Capsule

What Is the Bulk Mass Stack?

The Bulk Mass Stack takes a fundamentally different approach to our other stacks. Instead of separate bottles, this product combines four compounds into a single capsule: MK-677 Ibutamoren (10 mg), LGD-4033 Ligandrol (5 mg), RAD-140 Testolone (10 mg), and YK-11 Myostine (5 mg). This is the most aggressive stack in our range, designed for experienced researchers pursuing maximum anabolic stimulus through multiple independent pathways in a simplified dosing format.

If you’re looking to buy a bulk mass SARMs stack in the UK, sarms.co.uk supplies these all-in-one capsules at 99%+ HPLC-verified purity with full Certificates of Analysis, GMP-certified UK manufacture, and free next-day delivery. Whether you’re searching for a 4-in-1 SARM capsule UK, bulk mass SARM stack, YK-11 RAD-140 LGD stack, or the strongest SARMs stack available, this combination targets three independent growth pathways in a single daily capsule.

⚠️ Important: This stack combines three compounds that act on androgen receptors plus a GH secretagogue. It is designed for experienced researchers only. HPTA suppression is highly likely. YK-11 has the least human data of any compound in this stack: only in vitro (cell culture) studies exist. Researchers should have prior experience managing hormonal recovery protocols before using this product.

What’s in Each Capsule?

Compound	Dose Per Capsule	Classification	Mechanism	Human Trials
MK-677 Ibutamoren	10 mg	Growth hormone secretagogue	Ghrelin receptor agonist	Multiple (incl. Nass et al., 2008 – 2-year)
LGD-4033 Ligandrol	5 mg	Non-steroidal SARM	AR agonist	Phase I + Phase II (VK5211)
RAD-140 Testolone	10 mg	Non-steroidal SARM	AR agonist (~90:1 selectivity)	Phase I (Miller et al., 2022)
YK-11 Myostine	5 mg	Steroidal SARM / myostatin inhibitor	AR agonist + follistatin inducer	None (in vitro only)

90 capsules per bottle. One bottle per stack.

Why These Four Compounds? Three Independent Growth Pathways

The Bulk Mass Stack targets three mechanistically independent growth pathways simultaneously. This is not simply stacking more AR agonists for diminishing returns. Each pathway has a distinct biological target.

Pathway 1: Androgen Receptor Agonism (RAD-140 + LGD-4033)

RAD-140 and LGD-4033 are both potent non-steroidal SARMs that bind to androgen receptors in skeletal muscle and bone tissue, triggering downstream gene expression for protein synthesis and lean mass accrual. RAD-140 has higher binding affinity (~90:1 selectivity ratio), while LGD-4033 provides consistent anabolic drive at the 5 mg dose. Together, they create dense AR occupancy across different binding kinetics.

Pathway 2: Myostatin Inhibition via Follistatin (YK-11)

YK-11 is structurally unique among SARMs. It is steroidal (derived from DHT) and acts as both a partial AR agonist and an inducer of follistatin, a protein that inhibits myostatin. Myostatin is the body’s natural brake on muscle growth. By increasing follistatin expression, YK-11 theoretically removes this brake, targeting muscle growth through a mechanism independent of direct AR stimulation.

Evidence caveat: YK-11’s myostatin-inhibiting properties have been demonstrated in C2C12 myoblast cell cultures (Kanno et al., 2011) but have not been confirmed in animal models or human subjects. This remains the most theoretical component of the stack.

Pathway 3: GH/IGF-1 Axis (MK-677)

MK-677 elevates growth hormone and IGF-1 levels through ghrelin receptor activation. This pathway operates independently of both androgen receptors and myostatin/follistatin. MK-677 does not cause HPTA suppression and provides complementary support for recovery, sleep quality, and body composition.

Single Capsule Format: Advantages and Trade-offs

Advantages

Simplified dosing: One capsule per day instead of four separate products
Consistent ratios: Every dose delivers the same compound ratios (no accidental over- or under-dosing of individual compounds)
Convenience: Single bottle, single daily administration
Precise formulation: GMP-manufactured to deliver exact doses of all four compounds per capsule

Trade-offs

No dose flexibility: You cannot adjust individual compound doses. The ratios are fixed at 10/5/10/5 mg (MK-677/LGD/RAD-140/YK-11)
Cannot drop one compound: If you want to discontinue one component mid-cycle, you must stop taking all four
LGD-4033 at 5 mg (not 10 mg): Lower than the individual product dose, reflecting the multi-compound context
YK-11 at 5 mg (not adjustable): No ability to titrate the least-studied compound separately

If dose flexibility is important to your research, the Advanced Muscle Stack provides four separately bottled compounds (substituting clinically studied Ostarine for YK-11).

Bulk Mass Stack vs Advanced Stack: Which Is Right?

Feature	Bulk Mass Stack	Advanced Stack
Format	4-in-1 single capsule	4 separate bottles
AR agonists	RAD-140 + LGD-4033 + YK-11 (3, incl. steroidal)	RAD-140 + LGD-4033 + Ostarine (3, all non-steroidal)
YK-11 (myostatin pathway)	Yes (5 mg)	No
Ostarine	No	Yes (10 mg)
GH pathway	Yes (MK-677 10 mg)	Yes (MK-677 10 mg)
Growth pathways targeted	3 (AR + myostatin + GH)	2 (AR + GH)
Dose flexibility	None (fixed)	Full (separate bottles)
Human trial data	3 of 4 (YK-11 has in vitro only)	All 4 have human trials
Best for	Maximum potency, convenience	Maximum flexibility, evidence quality

Who Is the Bulk Mass Stack For?

Experienced researchers who have run multiple SARM cycles and understand HPTA suppression management
Those specifically interested in the myostatin inhibition pathway via YK-11’s follistatin mechanism
Researchers who prefer simplified dosing: one capsule per day instead of managing four separate products
Bulking-focused research protocols: the combination of three AR agonists + GH support is oriented toward maximum lean mass stimulus
Those comfortable with YK-11’s limited evidence base: in vitro data only, no animal or human studies

Who Should Consider Other Stacks?

Beginners: start with the Beginner Stack
Researchers prioritising evidence quality: the Advanced Stack uses all clinically trialled compounds
Those needing dose flexibility: Advanced or Intermediate stacks allow individual compound adjustment
Cutting/recomposition protocols: the fixed MK-677 dose increases appetite, which may be counterproductive

Dosage and Administration (Research Use Only)

Per capsule: MK-677 10 mg + LGD-4033 5 mg + RAD-140 10 mg + YK-11 5 mg
90 capsules per bottle
Administration: One capsule daily, oral
Typical research cycle: 8-12 weeks

The fixed-dose format means the compound ratios cannot be adjusted. The 5 mg doses of LGD-4033 and YK-11 reflect the multi-compound context where total AR load from three agonists is already substantial. The 10 mg doses of RAD-140 and MK-677 are standard individual-use reference doses.

For detailed information on each compound’s pharmacology and clinical dosing data, see the individual product pages:

MK-677 | LGD-4033 | RAD-140 | YK-11

Side Effects and Safety Considerations

HPTA Suppression: Near-Certain

Three AR agonists (RAD-140, LGD-4033, and YK-11) make HPTA suppression virtually guaranteed at the doses in this stack. Testosterone, LH, and FSH suppression will be significant. Robust PCT is not optional; it is essential.

YK-11-Specific Concerns

Steroidal structure: YK-11 is derived from DHT, making it structurally different from the other non-steroidal SARMs in this stack
Hepatotoxicity potential: Steroidal compounds generally have higher hepatotoxic potential than non-steroidal SARMs. No human liver safety data exists for YK-11
No human safety data: YK-11 has only been studied in cell cultures. All safety assumptions are theoretical

MK-677 Considerations

Increased appetite (ghrelin receptor activation): may be beneficial for bulking, counterproductive for cutting
Mild GH-mediated water retention (temporary, not oestrogenic)
Potential blood glucose/insulin sensitivity effects (documented in the Nass et al. 2-year trial)

Lipid and Liver Monitoring

Three concurrent AR agonists (one steroidal) warrant careful liver and lipid monitoring. Baseline, mid-cycle, and post-cycle blood panels are strongly recommended. HDL suppression is expected.

Does the Bulk Mass Stack Require PCT?

Yes, absolutely. Three AR agonists at these doses will produce significant HPTA suppression. PCT is essential. Pre-cycle blood work establishes your baseline; post-cycle blood work confirms recovery. MK-677 can be continued through PCT as it does not interact with the androgen axis.

YK-11’s steroidal structure may contribute to suppression differently than the non-steroidal SARMs. The lack of human data means the exact suppression profile of YK-11 in combination with RAD-140 and LGD-4033 is unknown.

Published Research on the Individual Compounds

Basaria S, et al. (2013). “The safety, pharmacokinetics, and effects of LGD-4033 in healthy young men.” J Gerontol A Biol Sci Med Sci, 68(1), 87-95. PMID: 22459616
Miller CP, et al. (2022). “Design, Synthesis, and Preclinical Characterization of RAD140.” ACS Med Chem Lett. PMID: 36368886
Kanno Y, et al. (2011). “Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression.” Biol Pharm Bull, 34(4), 554-557. PMID: 21467643
Nass R, et al. (2008). “Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults.” Ann Intern Med, 149(9), 601-611. PMID: 18981485

Why Buy the Bulk Mass Stack from sarms.co.uk?

99%+ HPLC-Verified Purity

Each batch of the all-in-one capsule is independently tested via HPLC by accredited third-party laboratories. Full COAs verify the identity, purity, and concentration of all four compounds in every capsule. Download the PDF directly from this page.

GMP-Certified UK Manufacture

Compounded in GMP-certified UK facilities with precise multi-compound formulation. Accurate dosing of four compounds in a single capsule requires pharmaceutical-grade manufacturing precision.

Precise Multi-Compound Dosing

Each capsule delivers exact doses of all four compounds. No measuring, no mixing, no dosing errors. The precision of capsule formulation eliminates the variability that comes with manually combining compounds.

Free Next-Day UK Delivery

All orders ship free with next-day UK delivery.

Frequently Asked Questions About the Bulk Mass Stack

Is this stack suitable for beginners?

No. This is the most aggressive stack in our range, combining three AR agonists with a GH secretagogue. It requires prior experience with individual SARMs, multi-compound protocols, and PCT management. Start with the Beginner Stack if you are new to SARMs research.

Why is YK-11 included instead of Ostarine?

YK-11 targets a different growth pathway (myostatin inhibition via follistatin) that is independent of direct AR agonism. This gives the stack three distinct growth mechanisms instead of two. The trade-off is that YK-11 has substantially less clinical evidence than Ostarine. The Advanced Stack uses Ostarine for researchers who prioritise evidence quality.

Can I adjust individual compound doses?

No. The single-capsule format delivers fixed doses of all four compounds. If dose flexibility is important, consider the Advanced Stack, which provides four separate bottles.

Why is LGD-4033 at 5 mg instead of 10 mg?

The lower LGD-4033 dose reflects the multi-compound context. With RAD-140 at 10 mg and YK-11 at 5 mg also providing AR activation, the total androgen receptor load is already substantial. The 5 mg LGD-4033 dose maintains its contribution to the stack without excessive AR saturation.

Is this the strongest stack you sell?

In terms of number of growth pathways targeted (three: AR agonism, myostatin inhibition, and GH secretion), yes. The Advanced Stack has broader AR coverage with three clinically studied SARMs but does not include the myostatin inhibition pathway.

How long should I cycle this stack?

Most research protocols reference 8-12 weeks. Given the complexity and suppression potential, many researchers favour the shorter end (8 weeks) for this stack to manage cumulative HPTA impact.

Will this stack cause water retention?

RAD-140, LGD-4033, and YK-11 do not aromatise and do not cause oestrogenic water retention. MK-677 may cause mild GH-mediated subcutaneous water retention in the first 2-4 weeks.

Can I add Cardarine to this stack?

Yes. Cardarine GW-501516 operates through PPAR-delta receptor activation for fat oxidation and endurance. It does not interact with androgen receptors, myostatin, or the GH axis, making it compatible without adding suppression or pathway interference.

What PCT do I need?

Three AR agonists at these doses require robust PCT. The specific protocol depends on the degree of suppression (confirmed via blood work). Pre-cycle, mid-cycle, and post-cycle blood panels are essential. MK-677 can be continued through PCT.

Is YK-11 safe?

There is no human safety data for YK-11. It has only been studied in cell cultures. Its steroidal structure (derived from DHT) raises theoretical hepatotoxicity concerns that have not been evaluated in vivo. Researchers using this stack accept a higher level of uncertainty regarding YK-11 specifically.

How does this compare to taking four separate products?

The compounds and doses are designed for a single-capsule format. The main difference is convenience (one capsule vs four) and the loss of dose flexibility. Quality and purity are identical to our individual products.

Can I run MK-677 separately after the cycle?

Not with this product, since all four compounds are in one capsule. If you want to continue MK-677 alone after the SARM cycle, purchase MK-677 Ibutamoren individually for the post-cycle and PCT period.

Disclaimers

This stack is sold strictly for laboratory and research purposes only
These products are not intended for human consumption
Not medicines, supplements, or food products
YK-11 has no human clinical trial data; all evidence is from in vitro cell culture studies
Not suitable for individuals under 18 years of age
Pregnant or breastfeeding women must not handle these compounds
Researchers should consult qualified professionals and adhere to all applicable regulations
sarms.co.uk does not provide medical advice and makes no claims regarding therapeutic outcomes
The content on this page does not constitute medical advice

Content last reviewed: 25 February 2026

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