Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.  The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.  Thus it is the challenge of competition among males of the species that facilitates aggression and violence.  Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.  The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males. 
Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.
In the Oxford Journal of Gerontology Series A: Biological Sciences and Medical Sciences, the popular nonsteroidal SARM LGD 4033 (Ligandrol) has been recently studied for it’s effectiveness and safety in healthy young men. Results were favorable indicated by hormone and lipid levels returning to normal without the use of a post cycle therapy. No dangers were detected throughout the study. although there was noticeable suppression in testosterone and HDL cholesterol, it was not significant enough to cause adverse reactions. Because LGD 4033 is considered one of the strongest and most potent nonsteroidal SARMs available, it is not likely that less potent SARMs will produce any harmful effects (Bhasin, 2010).