Injectable steroids are injected into muscle tissue, not into the veins. They are slowly released from the muscles into the rest of the body, and may be detectable for months after last use. Injectable steroids can be oil-based or water-based. Injectable anabolic steroids which are oil-based have longer half-life than water-based steroids. Both steroid types have much longer half-lives than oral anabolic steroids. And this is proving to be a drawback for injectables as they have high probability of being detected in drug screening since their clearance times tend to be longer than orals. Athletes resolve this problem by using injectable testosterone early in the cycle then switch to orals when approaching the end of the cycle and drug testing is imminent.
There’s also the possibility that testosterone injections can actually worsen some of the symptoms they are intended to treat. This is because the body will often respond to extra testosterone by assuming that it doesn’t need to produce more itself. Thus your testes will slow down their natural production of the hormone and you will actually end up with a lower ‘baseline’ when you aren’t receiving the injections. On the other hand, if all goes well you might see some side effects associated with a sudden peak in testosterone which include acne, hair loss, and short temper.