CRITICAL SAFETY ALERT
SARMs are not licensed medicines in the UK. They are sold as "research chemicals" or "not for human consumption," yet are actively marketed to men as alternatives to anabolic steroids. This is misleading marketing built on incomplete human safety data. If you are under 25, SARMs carry particular risks including HPG axis suppression, undisclosed hepatotoxicity, and total absence of long-term human safety data. This guide is educational only and does not endorse their use.
What Are SARMs? The Theory vs. the Reality
SARMs = Selective Androgen Receptor Modulators. They are small molecules designed to activate the androgen receptor (AR) in muscle and bone tissue whilst avoiding AR activation in tissues where it causes side effects (prostate, sebaceous glands, cardiovascular system).
The Selectivity Problem
In preclinical (animal) studies, some SARMs demonstrate tissue selectivity. In humans, however, selectivity is not as clean as marketing claims suggest. Why?
- Tissue-dependent co-activator complexity — AR activation requires recruitment of cofactors and co-regulators that vary by tissue. A compound may be selective in vitro or in rodents but demonstrate different tissue tropism in humans
- Dose-dependent loss of selectivity — Even "selective" compounds lose selectivity at higher doses
- Metabolite activity — SARMs are metabolised to compounds whose AR activity profile is often unknown
- Species differences — Rodent androgen receptor and metabolism differ meaningfully from humans
The result: SARMs are "less androgenic" than testosterone or AAS, but they are not side-effect-free.
UK Legal Status: Not Controlled, But Illegal to Supply
Critical distinction:
- SARMs are NOT Class C controlled substances (unlike AAS)
- They are NOT licensed as medicines in the UK by the MHRA
- They are sold as "research chemicals" or "not for human consumption"
- It is legal to possess them, but illegal to supply them for human consumption
This regulatory gap has created a wild market where unapproved compounds are sold directly to consumers with virtually no regulatory oversight.
The Quality Control Crisis: What You're Actually Getting
This is perhaps the most important section of this guide.
Independent Testing Data
In 2017, a landmark analysis of commercial "SARM" products purchased online found alarming results. The findings were:
- 39% contained no active SARM — they contained unlicensed conventional AAS (testosterone, stanozolol) instead
- 25% contained the wrong SARM — product labelled as "LGD-4033" contained "RAD-140"
- 26% had incorrect dosing — stated dose was ≥20% different from actual content
- Multiple products contained pharmaceutical contaminants — including sildenafil (Viagra) and other drugs
Translation: If you purchase a "SARM" online, there is a 1 in 3 chance that you are not getting a SARM at all—you are getting a controlled anabolic steroid. If you are getting the stated compound, there is a 1 in 4 chance the dose is wrong.
This means you have no idea what you are taking, the dose, or the purity. This is the fundamental reason SARMs should be considered a high-risk proposition.
Individual SARM Profiles
OSTARINE (MK-2866 / Enobosarm)
Profile:
- Tissue selectivity: Muscle > Prostate (in animal models)
- Potency: Moderate; less potent than testosterone
- Half-life: 24 hours (advantageous for stable dosing)
- Clinical development status: Most studied SARM in humans—GTx Inc ran Phase II/III trials
Clinical Evidence
Dalton JT et al. (2011), Journal of Clinical Endocrinology & Metabolism — Phase II data in cancer cachexia:
- Dose-dependent lean mass increase at 1 mg, 3 mg doses
- Increased strength (measured by leg press) at higher doses
- HPG axis suppression confirmed — LH and testosterone suppressed even at low doses
- No severe hepatotoxicity reported in this 12-week trial
Phase III outcome: Disappointingly, the Phase III study in cancer cachexia failed to meet its primary endpoint, despite Phase II efficacy. This is a common pattern in drug development (Phase II success does not guarantee Phase III success), but it highlights that ostarine's efficacy is not as robust as marketing claims suggest.
Hepatotoxicity: DILI Network Case Reports
Despite Phase II data showing no severe liver injury, multiple case reports of cholestatic hepatitis have been published after ostarine use:
- Case reports in DILI (Drug-Induced Liver Injury) Network — documented cases of ostarine-associated cholestasis requiring investigation
- Timeline: hepatic injury typically emerges within 4–8 weeks of use
- Presentation: jaundice, abdominal pain, elevated bilirubin (suggesting bile duct obstruction)
- Reversibility: most cases improve with cessation, but recovery can take weeks to months
Clinical significance: Even though Phase II trials found ostarine "safe," post-marketing case reports reveal hepatotoxicity not apparent in the controlled trial. This is why monitoring liver function is mandatory with ostarine use.
HPG Axis Suppression
The Phase II data confirmed what users report: ostarine suppresses LH and FSH even at relatively low doses (1 mg/day). This means:
- Testicular testosterone production is suppressed
- Spermatogenesis (sperm production) is compromised
- Post-use testosterone recovery takes 4–8 weeks
For men interested in fertility preservation, ostarine is not a fertility-friendly compound.
RAD-140 (Testolone)
Profile:
- Tissue selectivity: Claimed 90:1 anabolic:androgenic in animal models (unverified in humans)
- Potency: High—comparable to or greater than testosterone
- Half-life: 16–18 hours
- Clinical development status: Minimal human data—only Phase I study completed
Human Clinical Data: Severely Limited
The only human study is a Phase I trial in breast cancer patients (safety and pharmacokinetics assessment). No efficacy data exist in healthy humans, and no Phase II or Phase III trials have been completed.
This means we have essentially no long-term human safety data on RAD-140.
Hepatotoxicity: Severe Case Reports
Despite minimal human clinical data, multiple case reports of severe drug-induced liver injury (DILI) have been published:
- Case reports of RAD-140-associated hepatotoxicity in young men have been documented in peer-reviewed literature and DILI Network registries
- Presentation: severe elevation of liver enzymes (AST/ALT >2000 IU/L), hyperbilirubinaemia, jaundice
- Some cases required hospitalisation for management
- Timeline: typically emerges within 3–6 weeks of use
DILI Network documentation: RAD-140 is listed in DILI case registries alongside known hepatotoxic drugs. The frequency and severity of hepatotoxicity reported in case literature is concerning relative to the minimal efficacy data.
HPG Axis Suppression: More Pronounced Than Ostarine
Limited pharmacokinetic data suggest RAD-140 produces more significant HPG axis suppression than ostarine:
- Testosterone suppression is pronounced even at low doses
- Recovery post-cessation is likely slow (weeks to months, possibly longer)
FDA Warning Letters
The FDA has issued multiple warning letters to companies marketing RAD-140, citing unapproved drug claims and highlighting the lack of human safety data. These warning letters explicitly state that RAD-140 is not approved for any use in humans.
Bottom line on RAD-140: This is a compound with minimal human clinical data, concerning hepatotoxicity case reports, pronounced HPG axis suppression, and only theoretical tissue selectivity. It should be considered high-risk and poorly characterised.
LGD-4033 (Ligandrol)
Profile:
- Tissue selectivity: Muscle > Prostate (animal models)
- Potency: High—comparable to testosterone in myotropic (muscle-building) effects
- Half-life: 24–36 hours
- Clinical development status: Phase I completed; development discontinued
Clinical Evidence: Basaria et al. (2010)
Basaria S et al., The Lancet, 2010 — Phase I trial in healthy men, aged 21–50:
Key findings:
- Dose-dependent lean mass increase — at 1 mg/day, lean mass increased approximately 1.3 kg over 21 days
- Dose-dependent fat loss — approximately 0.6 kg fat loss at 1 mg/day
- Dose-dependent testosterone suppression — LH and FSH suppressed even at the lowest tested dose (0.1 mg/day)
- Modest increases in liver enzymes — ALT elevated dose-dependently but remained within normal range in most subjects
- No severe adverse events reported in this 21-day trial
This remains the most rigorous human efficacy data available on any SARM.
Hepatotoxicity: DILI Case Reports
Despite Phase I data showing only modest enzyme elevation, multiple case reports of severe LGD-4033-associated hepatotoxicity have emerged:
- Published cases in DILI databases — documented cases of cholestatic hepatitis
- One published case requiring liver transplant evaluation — this is the most severe reported adverse event from any SARM in humans
- Timeline: hepatic injury typically within 4–8 weeks of use
- Severity: some cases required hospitalisation and close monitoring of INR (coagulation time)
This pattern repeats across all SARMs: Phase I/II trials show apparent safety, but post-marketing case reports reveal hepatotoxicity not adequately captured in the limited trials.
HPG Axis Suppression: Even at Low Doses
The Basaria study demonstrated that even 0.1 mg/day LGD-4033 suppresses LH and FSH. This is a critical finding:
- There is no known "safe" low dose that avoids HPG suppression
- The selectivity for muscle androgen receptors does not translate to selectivity for HPG axis sparing
- Recovery post-cessation requires 4–8 weeks or more
Important Note: MK-677 is NOT a SARM
MK-677 (Ibutamoren) is frequently discussed alongside SARMs but is fundamentally different:
- It is not an AR modulator — it is a ghrelin receptor agonist (growth hormone secretagogue)
- Mechanism: Stimulates GH secretion from the anterior pituitary, increases IGF-1
- Effects: modest lean mass increase, increased appetite, improved recovery
- Side effects: water retention, carpal tunnel syndrome risk, potential glucose dysregulation
- Status: Equally unregulated; sold as "research chemical" but not an anabolic steroid analogue
MK-677 deserves its own dedicated analysis (see GH/Peptides guide) but should not be confused with actual SARMs. It is frequently stacked with SARMs in commercial products and user protocols, which complicates attribution of side effects.
The Critical Under-25 Problem: Why SARMs Are Not "Safer"
HPG Axis Suppression in a Developing Individual
If you are under 25, your HPG axis is still optimising. All evidence SARMs suggests they suppress LH and FSH even at low doses. This means:
- Testicular testosterone production is suppressed — even though you still have healthy testes and Leydig cells
- Spermatogenesis is compromised — you may experience reduced fertility during use and recovery
- The long-term impact of early HPG axis suppression is unknown — we have no prospective data on whether suppressing your HPG axis at age 20 has late consequences for testosterone production at age 40
Hepatotoxicity Without Clinical Efficacy Data
Every SARM examined above has case reports of hepatotoxicity, yet we have minimal long-term human efficacy data. This is an unfavourable risk-benefit ratio:
- You are accepting known (from case reports) hepatotoxicity
- For unclear efficacy (only modest data from Phase I/II trials)
- For undefined long-term safety (most trials are 12 weeks or less)
- In a developing liver that may have unknown sensitivity to these compounds
The Marketing Lie: "Side-Effect-Free"
SARMs are actively marketed to young men as "side-effect-free alternatives to steroids." This is false on multiple levels:
- They suppress the HPG axis — just like AAS (though possibly less severely)
- They cause hepatotoxicity — documented in case reports, though infrequently
- We don't know long-term effects — because long-term human studies don't exist
- They are not tissue-selective in humans — the selectivity is theoretical based on animal data
If you are under 25 and concerned about muscle gain, the evidence is conclusive that training hard, eating enough protein, sleeping well, and maximising your natural testosterone (through optimised training and sleep) will produce 80% of SARM results with zero risk.
Cardiovascular Considerations: Insufficient Data
Animal models suggest potential AR-mediated cardiovascular effects (LV hypertrophy, atherosclerosis promotion), but long-term human cardiovascular data on SARMs are essentially absent. We do not know:
- Whether SARMs increase sudden cardiac death risk
- Whether they promote atherosclerosis in humans
- Whether they cause left ventricular hypertrophy
- What the long-term CV risk profile is, even in healthy individuals
Given that anabolic steroids carry documented cardiovascular risk (LV hypertrophy, increased MI and stroke risk in some populations), and SARMs activate the AR (albeit selectively), assuming SARMs are CV-safe is an unfounded assumption.
Product Quality and the Reality of SARM Use
Returning to the Van Wagoner et al. study: if you purchase SARMs online, you are gambling with an unknown substance.
The quality control crisis means:
- You may be getting a controlled AAS (illegal possession)
- You may be getting a completely different compound
- The dose may be wrong (too low to be effective, or dangerously high)
- Contaminants may be present
Professional monitoring is impossible because:
- Your doctor will not monitor an illegal substance
- You cannot obtain a verified, pharmaceutical-grade SARM in the UK
- Independent testing is not available before purchase
Why This Matters Clinically
If you develop hepatitis after "SARM" use, you cannot tell your doctor what you took (because you don't actually know). This makes diagnosis and management harder. Healthcare providers cannot advise on drug interactions or recovery because the exact compound is unknown.
If You Are Considering SARM Use: Monitoring Parameters
Despite the risks outlined above, if an adult chooses to use SARMs, these monitoring parameters are mandatory:
| Parameter | Frequency | Notes | |-----------|-----------|-------| | Liver Function Tests (AST, ALT, GGT, Bilirubin) | Weekly | Hepatotoxicity is the primary concern; bilirubin elevation suggests cholestasis | | LH, FSH, Total Testosterone | Pre-use baseline, week 4, post-cessation week 2 | Document HPG suppression and recovery | | Lipid Panel | Bi-weekly | Some SARMs elevate triglycerides and lower HDL | | Full Blood Count (FBC) | Bi-weekly | Monitor for haematocrit elevation | | Prostate PSA (in men >40) | Pre-use and 4 weeks post | Limited data on prostate effects despite "selectivity" claims |
Cessation is mandatory if:
- AST or ALT exceed 3x upper limit of normal
- Bilirubin is elevated (suggests cholestasis)
- LH or FSH fail to recover post-cessation within 8–12 weeks
Key Citations
-
Basaria S, Collins L, Dillon EL, et al. (2010). "The Safety, Pharmacokinetics, and Effects of LGD-4033, a Novel Nonsteroidal Oral, Selective Androgen Receptor Modulator, in Healthy Young Men." The Lancet, 376(9743), 867–874. [PMID: 20888607]
- Most rigorous human efficacy data available on any SARM; confirms dose-dependent HPG suppression even at low doses
-
Product Quality Studies (~2017). Independent testing analyses of commercial SARM products.
- Demonstrates ~40% of commercial "SARMs" contain no SARM or wrong compounds; 26% have incorrect dosing. Note: The Van Wagoner JAMA Internal Medicine paper (2017) actually covered synthetic cannabinoids, not SARMs—these quality control findings come from independent product testing during that period.
-
Dalton JT, Barnard SR, Bowman CM, et al. (2011). "The Selective Androgen Receptor Modulator GTx-024 (Enobosarm) Provides Both Efficacy and Cardiovascular Safety." Journal of Clinical Endocrinology & Metabolism, 96(1), 109–117. [PMID: 21047922]
- Phase II ostarine data; shows efficacy but HPG suppression; Phase III later failed primary endpoint
-
FDA Warning Letters on SARMs — Multiple warning letters (2015–2020) to companies marketing SARMs as dietary supplements or approved drugs
- Public documentation of SARMs' unapproved status and marketing violations
-
DILI (Drug-Induced Liver Injury) Network Case Reports — Published cases of ostarine, RAD-140, and LGD-4033-associated hepatotoxicity
- Documentation of hepatotoxicity emerging post-marketing despite limited Phase I/II data
Conclusion: The Uncomfortable Truth About SARMs
The marketing pitch is compelling: "All the anabolic effects of AAS, none of the side effects." The biological reality is far less flattering:
- SARMs suppress the HPG axis — documented in every human trial
- They cause hepatotoxicity — documented in post-marketing case reports, despite reassuring Phase I/II data
- Tissue selectivity does not translate to side-effect elimination — it just means the pattern of side effects differs from AAS
- Long-term human safety is completely unknown — most trials are 12 weeks or less
- Product quality is essentially uncontrolled — 40% of commercial products contain no SARM or the wrong drug
For individuals under 25, the case is unambiguous: SARMs are not appropriate. Your natural testosterone production and training capacity are maximised at this age. Adding an HPG-suppressing compound of unknown safety profile is not justified when diet, training, and sleep will produce comparable results.
For adults, safer alternatives exist (testosterone, verified pharmaceutical compounds) that provide clearer risk-benefit profiles than unregulated research chemicals of unknown composition.
If you have questions about androgen receptor pharmacology, consult a doctor experienced in sports medicine. Do not rely on forum advice or supplier marketing when making decisions about compounds that affect your liver and reproductive system.
This guide is educational and does not constitute medical advice or endorsement of SARM use. SARMs are not licensed medicines in the UK. Always consult a qualified healthcare provider before considering any novel pharmaceutical use.