Trenbolone or Masteron: What Is the Difference

Trenbolone and masteron are united by the fact that neither is converted into estrogens. Because of this, informal sources often place them side by side as "dry" steroids. However, in chemical structure, receptor profile, history, and risks they differ substantially. The editorial team examines these differences on the basis of pharmacological data.

Where these substances come from

Trenbolone is a synthetic steroid developed in the 1960s. Its main legal use is veterinary: trenbolone acetate is used in the form of subcutaneous implants to accelerate muscle mass gain in cattle in countries where this is permitted. In the European Union the use of hormonal growth promoters in animal husbandry is prohibited.

For humans trenbolone was once produced in France in the form of the hexahydrobenzylcarbonate ester, but that drug was withdrawn from production long ago. Today there are no registered dosage forms of trenbolone for humans, and no modern clinical studies in humans either.

Drostanolone (masteron) was created as a medicinal product for humans: its propionate was used in the palliative therapy of advanced breast cancer in postmenopausal women. Later it was displaced by modern hormonal drugs, and in most countries it went out of circulation.

Thus, both substances now have no current medical indications for humans, but their origins differ: masteron was once a medicine, trenbolone primarily a veterinary agent.

Chemical structure and receptor profile

Trenbolone is 17β-hydroxyestra-4,9,11-trien-3-one. It belongs to the 19-nor derivatives, like nandrolone, but has three double bonds in the steroid skeleton. This structure makes the molecule rigid and provides a very high affinity for the androgen receptor.

Drostanolone is 2α-methyl-dihydrotestosterone, that is, a DHT derivative. Its affinity for the androgen receptor is moderate, and its anabolic action, according to early studies, is weaker than that of trenbolone.

An important difference is the progesterone receptor. Trenbolone, like other 19-nor derivatives, binds to it, whereas such activity is not characteristic of drostanolone. Progestogenic action enhances suppression of gonadotropins and may be linked to some of the side effects.

Neither of the two steroids is a substrate for aromatase. That is, estradiol is not formed from them, and classic estrogenic effects are not characteristic of them. However, this does not mean an absence of risks: with suppression of one's own testosterone, both can cause an estrogen deficiency.

Metabolism and tissue selectivity

The review by Yarrow, McCoy, and Borst (2010) summarizes data on trenbolone obtained mainly in rodents. In animal models trenbolone showed a pronounced anabolic effect on muscle and bone with a relatively lesser effect on the prostate than testosterone. The authors attribute this to the fact that 5α-reduction does not enhance its activity the way it does in the case of testosterone.

These data are often cited in athletic circles as evidence of trenbolone's "selectivity." However, it should be emphasized: these are the results of animal studies that cannot be directly transferred to humans, especially in the context of supraphysiological amounts and prolonged use.

Drostanolone, as a 5α-reduced molecule, does not interact with 5α-reductase at all. Its androgenic effects in the skin and hair follicles are due to its own activity at the receptor. Acne and acceleration of androgenic alopecia in predisposed people are considered typical.

Both substances in injectable form lack 17α-alkylation, so classic cholestatic hepatotoxicity is not the main problem for them. The main risks are associated with the cardiovascular and nervous systems.

Known and described side effects

Since there are no controlled studies of trenbolone in humans, information about its side effects in people comes from studies of anabolic steroid users, case reports, and surveys. This should be taken into account when assessing the data.

For trenbolone, the literature and user reports describe the following effects:

• pronounced suppression of the hormonal axis with a risk of prolonged hypogonadism;
• unfavorable changes in the lipid profile, in particular reduced HDL;
• sleep disturbances, increased sweating, irritability, and aggressiveness;
• a cough immediately after injection, described by users, the mechanism of which has not been definitively established;
• cardiovascular complications described in case reports, including cardiomyopathy.

For drostanolone, androgenic effects on skin and hair, suppression of the hormonal axis, and effects on lipids are considered typical. Psycho-emotional effects are described for androgens as a class, but drostanolone is mentioned in this context less often than trenbolone.

Shared for both is the risk of virilization in women and the fact that modern products come from the illegal market. Trenbolone for humans is often made from veterinary raw material, which adds risks regarding purity and sterility.

Large reviews, in particular the Endocrine Society statement (2014) and the review by Baggish and colleagues (2017), emphasize the cardiovascular toxicity of anabolic steroids as a class. There are no grounds to consider these two substances exceptions.

Detection and regulatory status

Both substances belong to section S1 of the WADA Prohibited List and are banned for athletes both in and out of competition. Their metabolites are identified by modern mass spectrometry methods.

Trenbolone also has regulatory significance in food safety: in EU countries residues of hormonal growth promoters in meat are monitored, and their use in animal husbandry is prohibited. In countries where implants are permitted, rules for their use have been established.

For humans trenbolone is not a medicinal product, so its circulation outside veterinary medicine is regulated in many jurisdictions by legislation on controlled substances or medicines. Drostanolone, as an anabolic steroid, is also subject to control in many countries.

Thus, from a regulatory standpoint both substances are outside legal medicine, and trenbolone additionally has a predominantly veterinary origin.

Editorial conclusions

Trenbolone and masteron do not aromatize, but the similarity ends there. Trenbolone is a 19-nor derivative with a very high affinity for the androgen receptor and progestogenic activity, masteron is a DHT derivative with moderate activity.

Data on trenbolone's "selectivity" were obtained in animals; for humans there are no controlled studies, and the effects described in users concern the heart, psyche, and hormonal axis.

Neither substance has medical indications for humans today, and the products come from the illegal market.

We also recommend reading our materials on the effects of anabolic steroids on the heart, on the psycho-emotional effects of androgens, and on why "dry" steroids are not safer.

References

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