Intramuscular testosterone undecanoate is available in the United States , Canada , Europe , and elsewhere in the world.    It is approved in over 100 countries worldwide.   Oral testosterone undecanoate is available in Canada, Europe, Mexico, Asia, and elsewhere but not in the United States.   Intramuscular testosterone undecanoate is marketed most commonly as Nebido in Canada and Europe and as Aveed in the United States while oral testosterone undecanoate is marketed most commonly as Andriol.   
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.