How safe is Trenbolone?

Thousands of bodybuilders inject themselves with trenbolone despite the fact that we know so little about the side effects of this anabolic steroid. That’s why Australian researchers tested trenbolone on rats, in the hope that it has the desirable features of testosterone but not the undesirable ones. If this turns out to be the case, then trenbolone might be useful for men who produce too little testosterone.


Many of the undesirable characteristics of testosterone are the work of estradiol and DHT, both products of testosterone conversion. Because trenbolone cannot convert into those metabolites, American researchers have suggested that trenbolone might be a SARM. [Steroids. 2010 Jun;75(6):377-89.]

According to Androgens and Anabolic Agents: Chemistry and Pharmacology by Julius Vida, trenbolone is a kind of super-nandrolone. Which means that studies where rats have been injected with trenbolone have shown that the relationship between trenbolone’s androgen and anabolic qualities is similar to that of nandrolone. But both the androgenic and anabolic effect of trenbolone are considerably stronger than those of nandrolone.

The figure below comes from Androgens and Anabolic Agents.


In 2002 American researchers compared the anabolic and androgenic effects of trenbolone with those of testosterone propionate. This study showed that trenbolone has noticeably fewer androgenic effects than testosterone propionate does. [Toxicol Sci. 2002 Dec;70(2):202-11.]

The Australian researchers implanted a pump in their rats, which released 2 mg trenbolone per kg bodyweight daily for six weeks. [TREN] Rats in a control group were given a pump with no active ingredients. [CTRL] The human equivalent of the dose studied is about 20-30 mg trenbolone per day.

At the end of the six weeks, the trenbolone rats were lighter than the animals in the control group. They had gained lean body mass and lost a fair amount of fat mass.



The trenbolone rats’ prostate however had become 49 percent larger than that of the rats in the control group. That sounds serious so the researchers examined the organ in minute detail. They found no inflammation or cancer cells.

This is probably because trenbolone reduced the estradiol level. Trenbolone also had the same effect on the rats’ testosterone level. Trenbolone had almost no effect on dimensions or structure of the testes, unlike the effects seen when testosterone is administered to rats in studies.

Trenbolone increased the rats’ insulin sensitivity – and therefore reduced the HOMA-IR. This is probably a result of the effect on body composition.


The level of triglycerides and LDL in the rats’ blood went down, which is a desirable effect. The HDL level decreased too, however, which is an undesirable effect.

The researchers detected no effects on liver enzymes. So in the dose tested, trenbolone is not dangerous for the liver.

“Further investigation into the comparative benefits conferred by trenbolone therapy relative to the current gold standard, testosterone, are well justified by these findings”, the researchers conclude. “Particularly in relevant models of obesity and metabolic dysregulation.”

Improvements in body composition, cardiometabolic risk factors and insulin sensitivity with trenbolone in normogonadic rats.


Trenbolone (TREN) is used for anabolic growth-promotion in over 20 million cattle annually and continues to be misused for aesthetic purposes in humans. The current study investigated TREN’s effects on body composition and cardiometabolic risk factors; and its tissue-selective effects on the cardiovascular system, liver and prostate. Male rats (n=12) were implanted with osmotic infusion pumps delivering either cyclodextrin vehicle (CTRL) or 2mg/kg/day TREN for 6 weeks. Dual-energy X-ray Absorptiometry assessment of body composition; organ wet weights and serum lipid profiles; and insulin sensitivity were assessed. Cardiac ultrasound examinations were performed before in vivo studies assessed myocardial susceptibility to ischemia-reperfusion (I/R) injury. Circulating sex hormones and liver enzyme activities; and prostate and liver histology were examined. In 6 weeks, fat mass increased by 34±7% in CTRLs (p<0.01). Fat mass decreased by 37±6% and lean mass increased by 11±4% with TREN (p<0.05). Serum triglycerides, HDL and LDL were reduced by 62%, 57% and 78% (p<0.05) respectively in TREN rats. Histological examination of the prostates from TREN-treated rats indicated benign hyperplasia associated with an increased prostate mass (149% compared to CTRLs, p<0.01). No evidence of adverse cardiac or hepatic effects was observed. In conclusion, improvements in body composition, lipid profile and insulin sensitivity (key risk factors for cardiometabolic disease) were achieved with six-week TREN treatment without evidence of adverse cardiovascular or hepatic effects that are commonly associated with traditional anabolic steroid misuse. Sex hormone suppression and benign prostate hyperplasia were confirmed as adverse effects of the treatment.

PMID: 25554582 [PubMed – in process]