Pain due to route of administration
Pain due to the substance being injected
Within these two categories there are further sub-groups for causes of injection pain, and these will be discussed in further detail.

Pain due to route of administration
Invasiveness of Injection. The initial cause of injection pain that may be experienced is quite simply the fact that an IM injection itself is an invasive procedure, in that the body's natural barrier of skin is being penetrated by a sharp needle and any further cellular content along the needle's path is being sheared. This in itself, although relatively invasive, can cause some pain. This pain tends to be initial, however due to the design of sterile needles for injection, the curved nature of the needle point allows for minimal pain, and thus this is not a common cause of post-injection pain.
Opening a new IM injection site. When a new muscular site is invaded and a volume of substance is injected therein, there is often some soreness associated with such an injection. The muscle group is not used to containing an additional volume of a substance, thus pain can result. This is usually only experienced when a site is first used for an IM injection. This is why when using a new site it is encouraged to inject a smaller amount initially, from 0.5-1ml dependent upon muscle size. Such pain and soreness usually ceases after a site has received at least one injection.
Physical location of injection. Often when injecting a substance, the physical location, that is where the needle releases the substance, can result in discomfort after the injection. This is most likely due to the substance (especially if oil based and slowly absorbed) sitting in between muscle groups or in a small muscle, as this will cause more pain than being injected into the middle of a muscle or a larger muscle. This can happen from time to time even with experienced users.
Volume of substance injected. Tying in with point 1(ii), the volume of injection will also make a significant difference to any soreness and pain experienced. Generally larger volumes are better tolerated in larger muscle groups (gluteus, quadriceps, etc), with smaller muscle groups (biceps, triceps, etc) fair better with smaller volumes (<2ml). As you increase the volume injected, you increase the amount of substance contained within the muscle that is normally present, thus you increase the risk of an inflammatory response and soreness. Very large volumes (>5-6ml, especially of oil-based substances) are not advised due to the risk of developing a sterile abscess.
Pain due to the substance being injected
Abscess development. As with any substance, unless it is sterile (and even in sterile cases bacteria on skin and body hair may be pushed past the skin barrier inside the body by the injection procedure) there is a high risk of developing an internal infection known as an abscess. This will result in large amount of swelling, redness, flu-like symptoms and increased lymphocytes thus increased inflammation resulting in a fair degree of pain experienced. The risk of such infections being developed when using completely sterile products however is very low.
Solvent concentration of substance. The concentration and type of solvents used in the preparation of the substance to be injected will affect any pain and soreness that will be experienced post-injection. Certain buffers and solvents used when injected in pure form give a fair amount of soreness. For example, some peptides are suspended in 100mM acetic acid, which when injected even in small amounts can give the user some discomfort. It is an important point to make that pain resulting from solvent concentrations used is most likely to commence quite soon after the injection, from a few minutes to a few hours maximum. Pain that takes longer than this to develop is usually due to other factors discussed here.

Another common solvent used as a preservative in anabolic steroid and other IM injection preparations, is benzyl alcohol (BA). At high concentrations, BA will cause injection pain in the vast majority of users. However in concentrations <10% BA, most will experience little discomfort due to BA. Many people claim that underground laboratories that make injectable anabolic steroids in a non-regulated manner use high BA percentages in their products such as testosterone propionate which is why users experience pain. However, as explained here and in point 2(iii), the BA is unlikely to be the cause of pain. This is why it should be noted that in actual fact, many pharmaceutical preparations contain higher than expected amounts of BA in them. Deca-Pronabol, a pharmaceutically produced form of nandrolone decanoate, contains 9% BA and users generally report no pain associated with its injection. Some preparations of Sustanon-250 by established pharmaceutical companies are made with 10% BA (0.1ml BA per 1.0ml ampoule). However, many would here argue that Sustanon-250 is a sore injection for many. Despite this, when one looks at the make-up of the active ingredients of Sustanon-250, we see a combined testosterone propionate and phenylpropionate amount of roughly 100mg/ml. For reasons discussed in part 2(iii), we may safely assume that the pain is more likely to occur due to the high concentration of these short esters, as opposed to merely high BA concentration. However, it is worth remembering that everyone reacts differently to various solvents and 10% BA may not cause pain for many users, but it will cause soreness for a significant percentage of other users. Other solvents within the preparation apart from the ones outlined here can also contribute or cause injection pain; however the ones discussed are the most significant in the context of anabolic steroid preparations.

Concentration of active product. This is probably the most prevalent cause of post-injection pain experienced by anabolic steroid users. This is most likely due to the demand for underground laboratories to produce more concentrated steroid preparations (high mg/ml of hormone) to reduce number and volumes of injections. One good example of this is the production of testosterone propionate by many different labs. If we look at the preparation of testosterone propionate by legitimate pharmaceutical companies, we see that the maximum concentration normally produced is 50mg/ml. Despite this, most underground labs today will produce multi-use vials of testosterone propionate that are at a minimum of 100mg/ml. Hormones that contain short esters on them (like acetate, propionate, phenylpropionate) have a much higher melting point and thus cannot be made as concentrated as those with longer esters (enanthate, decanoate, etc). Although testosterone propionate can be effectively made in standard amounts of solvents and oil to 100mg/ml without crashing out of this solution, once injected in the body, the solvents tend to leach out of the solution very quickly, being absorbed much quicker than the oil. This leaves behind oil and hormone in the muscle, and at the higher concentrations (which rely on solvents to not crash in solution) this will result in some of the hormone crashing out of solution to give crystals. These crystals cause significant muscular discomfort, and also can result in the recruitment of lymphocytes involved in inflammation thus the area around the crystals can get inflamed with a build up of blood cells. This takes time to dissipate and longer for the crystals to be absorbed into the body, which is why this type of pain and discomfort usually lasts for several days.
It should be noted however that there are certain carriers and solvents which allow for higher mg/ml preparations to be made that result in the reduction of pain. One solvent occasionally used is guaicol, which allows for more concentrated solutions to be produced and also acts as a slight analgesic or pain reliever at the site of injection. A more useful lipid carrier as an alternative to a normal oil carrier is ethyl oleate (EO). EO can be substituted for other carrier oils, and is a less viscous (thinner) carrier that also allows more of the hormone to be dissolved in it compared with other oils. The safety of EO for injections in humans is often questioned; however several different pharmaceutically produced injection products have been made that use EO as a carrier, most notably Farmak testosterone propionate. Furthermore, ethanol (alcohol) is converted to several products in the body when ingested, one being oleic acid. One potential issue with the use of EO however, is that a small percentage of users may experience an allergic-type reaction to its use, typified by a rash and some local discomfort, yet this is a more rare reaction to EO.

Below is a list of common anabolic steroids and when prepared with common percentages of solvents and normal oil carriers (not EO), what the maximum normal concentration that can be achieved before pain is experienced:
Testosterone Propionate <100mg/ml
Testosterone Enanthate <300mg/ml
Testosterone Cypionate <250mg/ml
Nandrolone Decanoate <325mg/ml
Nandrolone Phenylpropionate <150mg/ml
Trenbolone Acetate <100mg/ml
Trenbolone Enanthate <250mg/ml
Boldenone Undecylenate (EQ) <900mg/ml
Methenolone Enanthate <75mg/ml
Drostanolone Propionate <150mg/ml

In summary, there are various different causatives of IM pain post-injection, however the most prevalent is likely to be the concentration of hormone used in the preparation and secondly to a lesser extent, the concentration of solvents used. However as outlined, with any injection this is an invasive procedure with regards to breaking the body's natural barriers, there is always a risk of soreness and discomfort

From CC

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Disclaimer: Hypermuscles.com does not promote the use of anabolic steroids without a doctor's prescription. The information we share is for entertainment and research purposes only.