Anabolic steroids differ in their characteristics, which means there are steroids that are only suitable for specific uses. For instance, Trenbolone is not recommended for bulking but it is an outstanding fat burner. This makes it perfect for a lean mass cycle or a cutting cycle. Always take the side effects of a particular compound into consideration whenever you plan a stack. Do not combine anabolic steroids that show similar side effects. For example, never combine Anapolon and Dianabol because they are already quite toxic and if you combine them, the toxicity will increase exponentially and cause serious damage to your body.
The most commonly used AAS in medicine are testosterone and its various esters (but most commonly testosterone undecanoate , testosterone enanthate , testosterone cypionate , and testosterone propionate ),  nandrolone esters (most commonly nandrolone decanoate and nandrolone phenylpropionate ), stanozolol , and metandienone (methandrostenolone).  Others also available and used commonly but to a lesser extent include methyltestosterone , oxandrolone , mesterolone , and oxymetholone , as well as drostanolone propionate , metenolone (methylandrostenolone), and fluoxymesterone .  Dihydrotestosterone (DHT; androstanolone, stanolone) and its esters are also notable, although they are not widely used in medicine.  Boldenone undecylenate and trenbolone acetate are used in veterinary medicine . 
As an example, should you choose to run a cycle that includes both Dianabol and Anavar, you will need to be extremely careful when it comes to overlapping them. The two are both hepatotoxic, which means they will cause liver damage. You will need to consider this carefully when it comes to choosing cycle lengths. If you take Dianabol for four weeks at the beginning of your cycle, then make the switch to Anavar, you should limit your Anavar use to four weeks, as well. This reduces your entire cycle time to eight weeks, which helps to alleviate some of the risk of liver damage.