Anabolic-androgenic steroids are organic compounds that hold a chemical structure characterized by a particular arrangement. Every steroid compound is different based on specific structural variables.
 
Naturally, there are many different types of steroids, the majority of which have no muscle-building effect, strength, or athletic performance whatsoever. As a matter of fact, many of those destroy and break down muscle tissue, such as corticosteroids.
The human body naturally produces different types of steroids such as Cholesterol, Cholecalciferol (Vitamin D), Estrogen, Testosterone, and Cortisol. One interesting fact is that Vitamin D is actually a steroidal molecule but contains a broken chemical ring. Even more interesting is that Cholesterol is the base steroidal compound or the precursor that the body’s cells use to synthesize all other steroids
Testosterone is the primary anabolic steroid manufactured in every human body and in most animal species. It is the male sex hormone that provides the male gender with male traits and characteristics. This hormone is responsible for controlling the maintenance of many different functions in the human body, one of which is muscle fiber growth. Another Two naturally produced anabolic steroids in humans are Dihydrotestosterone (DHT) and Nandrolone. These are the three main anabolic steroids from which all other anabolic steroids are derived.
It safe to say that all anabolic steroids in existence are basically modified forms of Testosterone, Dihydrotestosterone, or Nandrolone. These modified variants are called analogs and derivatives.
Even more, Testosterone is quite literally the original and primary hormone and which every single anabolic steroid is derived from.
Based on the aforementioned fact, we can essentially categorize anabolic androgenic steroids as:
1. Testosterone analogs and derivatives
2. Dihydrotestosterone analogs and derivatives
3. Nandrolone analogs and derivatives
 
Testosterone is transformed into Dihydrotestosterone in the human body because of an enzyme called 5-alpha reductase (5AR), and even more, Nandrolone is a by-product of the aromatization of Testosterone into Estrogen.
Naturally theoretically, every derivative will often take on the same properties and characteristics of its parent hormone. For example, all Dihydrotestosterone (DHT) derivatives inherit the inability to convert into Estrogen because of the inability to interact with the aromatase enzyme. But this inheritance of the same traits most often exists in theory. However, in practice, the opposite may be the truth or at least a differing effect. This is because once an anabolic steroid is modified, the new analog is, in reality, a totally different hormone with unique properties and it may or may not share characteristics with its parent hormone.
Testosterone is usually modified and altered to create variants that could display different effects in the body that may be more beneficial in certain areas of function. Such modifications would allow a particular anabolic steroid analog to be more preferable to treat a certain condition or disease in medicine than Testosterone itself would be able to. Other aims for those modifications of Testosterone are for the purpose of producing different anabolic steroid derivatives for more convenient anabolic steroid suitable for various individuals or genders or for example, for patients suffering from debilitations and diseases whereby Testosterone itself may worsen an individual’s medical condition in a certain area. The other reason is essentially to minimize the undesired side effect that may or may not occur when utilizing Testosterone, by creating a milder side effect profile steroid.
Those were the medical reason for such modifications. However, when the purpose of anabolic steroids is performance and physique enhancement, the idea behind the modification and the use of different anabolic steroid types is very different and somehow clear. The first obvious reason is the discovery of an anabolic steroid analog that would exhibit a stronger anabolic effect than Testosterone, and of course with a less negative side effect profile which makes it more preferable to any athlete.
For example, Testosterone may result in water retention because of the ability to aromatize into Estrogen. Such an effect might not be a concern for a strength athlete or a powerlifter, However, this is not at all beneficial for other athletes whose main goal is speed such as sprinting. Instead, a sprinter.
One more thing to be considered is that all these analogs and because of the above-mentioned modifications, all anabolic androgenic steroids differ in their ability to bind to the androgen receptor and therefore can be categorized into Class 1 and Class 2, Class 1 being the one with the strongest binding affinity to the receptor. This is where the idea of stacking stems from. When stacking or combining 2 or 3 steroids together in a cycle, the athlete is able to increase the synergistic effects between the anabolic steroids to create a highly anabolic environment or to reach a specific goal.
Another fact of extreme importance is that Testosterone is always considered the reference point when measuring any other anabolic steroid strength and effect in regards to the androgenic and anabolic abilities, much like the Celsius scale of temperature measurement where the freezing point and boiling points of water are used as the baseline measurements for temperature. Testosterone’s anabolic and androgenic ratings are both 100.
Based on their mode of application, there exist Two types of steroids. Oral and injectables.
 
Injectable anabolic androgenic steroids are manufactured in an used as deep intramuscular injections containing various oils and, in a few cases, sterile water. The active hormone or compound is suspended in the oil or water solution.
The hormone is more often than not is attached to another chemical substance called Ester to prolong and delay the release of the hormone into the bloodstream and consequently prolong its effects.
Injectable AAS have 2 advantages when compared to oral steroids. First, they have a  longer-lasting active- lives (the period in which the AAS remains active in the body). Injectables usually have the active-life from 1 day to 4 weeks. Second, injectables do not go through the first-pass deactivation which takes place in the small intestines and liver but are eventually deactivated by the liver as well. However, it should be noted that injectables are much easier on the liver even in much higher dosages and therefore much more favorable by athletes and bodybuilders.
Some of the most widely used and well-known injectable steroid is, of course, the granddaddy of all other steroids which is Testosterone with all its esters. Testosterone Propionate, Testosterone Enanthate, Testosterone Cypionate, and also testosterone Suspension or without ester.
As well as Nandrolone with all its ester such as Nandrolone Decanoate (Deca Durabolin), and Nandrolone Phenylpropionate (NPP).
Equipoise (Boldenone) which can be described as an injectable Dianabol without the methyl group.
Primobolan Depot, which one of the cleanest and most favorable steroids due to the mild side effect profile.
 Drostanolone and its esters such as Masteron Propionate and Masteron Enanthate, which are Dihydrotestosterone analogs and derivatives.
Trenbolone and its esters such as Trenbolone Acetate, Trenbolone Enanthate and Trenbolone Hexahydrobenzylcarbonate. Those are basically the only Nandrolone derivatives that are conventionally and commercially available.
One interesting fact is that Nandrolone and Trenbolone belong to a special unique category of anabolic steroids known as Progestins. Nandrolone itself is quite structurally similar to Testosterone. However, Nandrolone is distinctive from Testosterone by the absence of the 19th carbon. Consequently, Nandrolone and Trenbolone are known as 19-nortestosterone compounds.
One last but very important note concerning all anabolic androgenic steroids in both forms, Oral or Injectables is that there is NO such a thing as Anabolic Steroids for Bulking and different ones for Cutting. This is simply a myth.
Anabolic steroids do not directly burn fat, rather they instead simply increase nutrient partitioning which is directing/shuttling ingested nutrients, vitamins, and minerals towards muscle repair and muscle growth to the degree that fat in the body is completely avoided. Anabolic steroids do not have any direct impact on lipolysis that would result in a dramatic reduction. Rather, they interact with androgen receptors on fat tissue to initiate lipolysis (fat breakdown), but this does not occur to any particularly high degree.
The effect of any steroid whether it is fat burning or bulking and muscle mass gains is 100% dependent on the individual’s nutrition and training. Different kinds of steroids simply help to accentuate the efforts and hard work that the nutrition and training aspects have properly achieved.