Some bodybuilders and athletes use trenbolone esters for their muscle-building and otherwise performance-enhancing effects.  Such use is illegal in the United States and many other countries. The DEA classifies trenbolone and its esters as Schedule III controlled substances under the Controlled Substances Act .  Trenbolone is classified as a Schedule 4 drug in Canada  and a class C drug with no penalty for personal use or possession in the United Kingdom .  Use or possession of steroids without a prescription is a crime in Australia . 
It was reported in 2002 that tibolone or its metabolite δ 4 -tibolone is transformed by aromatase into the potent estrogen 7α-methylethinylestradiol in women, analogously to the transformation of norethisterone into ethinylestradiol .  Controversy and disagreement followed when other researchers were unable to reproduce the findings however.       By 2008, it was established that tibolone is not aromatized in women and that the previous findings of 7α-methylethinylestradiol were merely a methdological artifact.    In accordance, a 2009 study found that an aromatase inhibitor had no effect on the estrogenic potencies of tibolone or its metabolites in vitro , unlike the case of testosterone .  In addition, another 2009 study found that the estrogenic effects of tibolone on adiposity in rats do not require aromatization (as indicated by the use of aromatase knockout mice ), further in support that 3α-hydroxytibolone and 3β-hydroxytibolone are indeed responsible for such effects. 
Anabolic steroid implants are allowed for veterinary use. But if someone diverts this for use in humans, it will be deemed as a distribution of a Schedule III drug leading to prosecution. The law on trenbolone differs in other countries. For instance, in Canada it is a Schedule IV drug. In Canada, all anabolic steroids are classified as Schedule IV drugs. In the UK, anabolic steroids are classified as Class C substances. Their possession can lead to a 2 year jail term, while their production and supply can lead to a 14 year jail term. But many countries do not have strict laws. In some places, you can even buy it over the counter.