In theory, injectable steroids are safer to take because they do not have to be digested (as oral steroids do). People that consider taking steroids generally have the problem that they will not be able to inject the drug into themselves. This makes oral steroids very popular in the underground bodybuilding community. Oral steroids are said to be harder on the liver than injectable steroids. This is proven to be true. Oral steroids have a shorter “half-life” than injectable steroids. A “half-life” basically is how long a steroid stays in your system. Because of the shorter “half lives” of oral steroids, they only last 3-5hours per pill. Therefore, oral steroids need to be taken several times a day. This puts immense strain on the liver.
Most pills/oral tabs/oral liquids tend to be 17 alpha-alkylated steroids. They have a methyl group located at the 17th carbon location. This is done so the steroid can stay active through first-pass metabolism by the liver. As a result, oral steroids are harder on your liver than injectibles. That is why people advise limiting there use to 4-6 weeks on average. Injectibles, in contrast, don't have nearly the same influence on your liver function (the steroid bypasses first pass metabolism by the liver when injected, but is still eventually processed there to a lesser degree). For this reason, injectibles are typically considered safer, and can be used for much longer peroids of time than orals - like months as compared to weeks.
BTW, examples of 17-aa oral steroids are dianabol (dbol), anadrol (abombs), winstrol tabs, anavar, halotestin, and methyltestosterone.
Hope this helps bro
