Testosterone isobutyrate is an injectable steroid preparation that contains the isobutyrate ester of testosterone in a water base. Among bodybuilders, testosterone isobutyrate is often considered analogous to testosterone suspension (no ester). Although both are usually found as water-based suspensions, the pharmacokinetics of the two products are admittedly very different. While testosterone (free) suspension is very fast-acting, requiring injections to be given every few days, testosterone isobutyrate is much slower to release, and is usually administered once every two weeks in a clinical setting. As an injectable testosterone, testosterone isobutyrate is favored for its ability to promote rapid gains in muscle mass and strength.
|Brand name||Agovirin Depot|
Testosterone Isobutyrate History
Injectable testosterone isobutyrate microcrystal suspension was first described in 1952. This agent was developed in an effort to create an injectable (depot) form of testosterone that would be slower acting that regular (free) testosterone suspension would emerge as the dominant slow-acting injectable testosterone, and the isobutyrate ester would ultimately see little commercial success.
The only modern steroid product to use testosterone isobutyrate is Agovirin Depot, developed by Biotika in Czechoslovakia. It is primarily prescribed to treat males with insufficient androgen levels and adolescents with delayed puberty, although it is indicated for a variety of other purposes including the treatment of Klinefelter syndrome (a disease where an extra chromosome results in an imbalance of androgenicity and estrogenicity), aplastic anemia, Cushing’s syndrome (as an anabolic agent to preserve lean tissue), postmenopausal osteoporosis, advanced breast cancer, mastodynia (breast pain), and cachexia (wasting of the body due to severe illness). Agovirin Depot is still produced by Biotika (currently in the Slovak Republic), and remains a popular export to European black markets.
How is Testosterone Isobutyrate Supplied
Testosterone isobutyrate suspension is available on the human drug market in the Slovak Republic as Agovirin Depot (Biotika). It contains 25 mg/ml of steroid mixed in a waterbased solution; packaged in a 2 ml ampule (5 ampules per box). Testosterone isobutyrate has low water solubility; the steroid will noticeably separate from the water-based solution when an ampule is left to sit. A quick shake will temporarily place the drug back into suspension, so that the withdrawn dosage should always be consistent.
Structural Characteristics of Testosterone Isobutyrate
Testosterone isobutyrate is a modified form of testosterone, where a carboxylic acid ester (2-methyl propionic acid) has been attached to the 17-beta hydroxyl group. Esterified forms of testosterone are less polar than free testosterone, and are absorbed more slowly from the area of injection. Once in the bloodstream, the ester is removed to yield free (active) testosterone. Esterified forms of testosterone are designed to prolong the window of therapeutic effect following administration, allowing for a less frequent injection schedule compared to injections of free (unesterified) steroid. Testosterone isobutyrate microcrystalline suspension is designed to provide physiological androgen concentrations for approximately 2 weeks following injection.
Testosterone Isobutyrate Side Effects (Estrogenic)
Testosterone is readily aromatized in the body to estradiol (estrogen). The aromatase (estrogen synthetase) enzyme is responsible for this metabolism of testosterone. Elevated estrogen levels can cause side effects such as increased water retention, body fat gain, and gynecomastia. Testosterone is considered a moderately estrogenic steroid. An anti-estrogen such as clomiphene citrate or tamoxifen citrate may be necessary to prevent estrogenic side effects. One may alternately use an aromatase inhibitor like Arimidex (anastrozole), which more efficiently controls estrogen by preventing its synthesis. Aromatase inhibitors can be quite expensive in comparison to anti-estrogens, however, and may also have negative effects on blood lipids.
Estrogenic side effects will occur in a dose-dependant manner, with higher doses (above normal therapeutic levels) of testosterone more likely to require the concurrent use of an antiestrogen or aromatase inhibitor. Since water retention and loss of muscle definition are common with higher doses of testosterone, this drug is usually considered a poor choice for dieting or cutting phases of training. Its moderate estrogenicity makes it more ideal for bulking phases, where the added water retention will support raw strength and muscle size, and help foster a stronger anabolic environment.
Testosterone Isobutyrate Side Effects (Androgenic)
Testosterone is the primary male androgen, responsible for maintaining secondary male sexual characteristics. Elevated levels of testosterone are likely to produce androgenic side effects including oily skin, acne, and body/facial hair growth. Men with a genetic predisposition for hair loss (androgenetic alopecia) may notice accelerated male pattern balding. Those concerned about hair loss may find a more comfortable option in nandrolone decanoate, which is a comparably less androgenic steroid. Women are warned of the potential virilizing effects of anabolic/androgenic steroids, especially with a strong androgen such as testosterone. These may include deepening of the voice, menstrual irregularities, changes in skin texture, facial hair growth, and clitoral enlargement.
In androgen-responsive target tissues such as the skin, scalp, and prostate, the high relative androgenicity of testosterone is dependant on its reduction to dihydrotestosterone (DHT). The 5-alpha reductase enzyme is responsible for this metabolism of testosterone. The concurrent use of a 5-alpha reductase inhibitor such as finasteride or dutasteride will interfere with site-specific potentiation of testosterone action, lowering the tendency of testosterone drugs to produce androgenic side effects. It is important to remember that anabolic and androgenic effects are both mediated via the cytosolic androgen receptor. Complete separation of testosterone’s anabolic and androgenic properties is not possible, even with total 5-alpha reductase inhibition.
Testosterone Isobutyrate Side Effects (Hepatotoxicity)
Testosterone does not have hepatotoxic effects; liver toxicity is unlikely. One study examined the potential for hepatotoxicity with high doses of testosterone by administering 400 mg of the hormone per day (2,800 mg per week) to a group of male subjects. The steroid was taken orally so that higher peak concentrations would be reached in hepatic tissues compared to intramuscular injections. The hormone was given daily for 20 days, and produced no significant changes in liver enzyme values including serum albumin, bilirubin, alanine-amino-transferase, and alkaline phosphatases.
Testosterone Isobutyrate Side Effects (Cardiovascular)
Anabolic/androgenic steroids can have deleterious effects on serum cholesterol. This includes a tendency to reduce HDL (good) cholesterol values and increase LDL (bad) cholesterol values, which may shift the HDL to LDL balance in a direction that favors greater risk of arteriosclerosis. The relative impact of an anabolic/androgenic steroid on serum lipids is dependant on the dose, route of administration (oral vs. injectable), type of steroid (aromatizable or non-aromatizable), and level of resistance to hepatic metabolism. Anabolic/androgenic steroids may also adversely effect blood pressure and triglycerides, reduce endothelial relaxation, and support left ventricular hypertrophy, all potentially increasing the risk of cardiovascular disease and myocardial infarction.
Testosterone tends to have a much less dramatic impact on cardiovascular risk factors than synthetic steroids. This is due in part to its openness to metabolism by the liver, which allows it to have less effect on the hepatic management of cholesterol. The aromatization of testosterone to estradiol also helps to mitigate the negative effects of androgens on serum lipids. In one study, 280 mg per week of testosterone ester (enanthate) had a slight but not statistically significant effect on HDL cholesterol after 12 weeks, but when taken with an aromatase inhibitor a strong (25%) decrease was seen. Studies using 300 mg of testosterone ester (enanthate) per week for 20 weeks without an aromatase inhibitor demonstrated only a 13% decrease in HDL cholesterol, while at 600 mg the reduction reached 21%. The negative impact of aromatase inhibition should be taken into consideration before such drug is added to testosterone therapy.
Due to the positive influence of estrogen on serum lipids, tamoxifen citrate or clomiphene citrate are preferred to aromatase inhibitors for those concerned with cardiovascular health, as they offer a partial estrogenic effect in the liver. This allows them to potentially improve lipid profiles and offset some of the negative effects of androgens. With doses of 600 mg or less of testosterone per week, the impact on lipid profile tends to be noticeable but not dramatic, making an anti-estrogen (for cardioprotective purposes) perhaps unnecessary. Doses of 600 mg or less per week have also failed to produce statistically significant changes in LDL/VLDL cholesterol, triglycerides, apolipoprotein B/C-III, C-reactive protein, and insulin sensitivity, all indicating a relatively weak impact on cardiovascular risk factors. When used in moderate doses, injectable testosterone esters are usually considered to be the safest of all anabolic/androgenic steroids.
To help reduce cardiovascular strain it is advised to maintain an active cardiovascular exercise program and minimize the intake of saturated fats, cholesterol, and simple carbohydrates at all times during active AAS administration. Supplementing with fish oils (4 grams per day) and a natural cholesterol/antioxidant formula such as Lipid Stabil or a product with comparable ingredients is also recommended.
Testosterone Isobutyrate Side Effects (Testosterone Suppression)
All anabolic/androgenic steroids when taken in doses sufficient to promote muscle gain are expected to suppress endogenous testosterone production. Testosterone is the primary male androgen, and offers strong negative feedback on endogenous testosterone production. Testosterone-based drugs will, likewise, have a strong effect on the hypothalamic regulation of natural steroid hormones. Without the intervention of testosterone stimulating substances, testosterone levels should return to normal within 1-4 months of drug secession. Note that prolonged hypogonadotrophic hypogonadism can develop secondary to steroid abuse, necessitating medical intervention.
Testosterone Isobutyrate Administration (General)
The design of testosterone isobutyrate (as Agovirin Depot) is slightly different than that of most testosterone esters, which are usually made as oily solutions. Agovirin Depot instead contains a microcrystalline aqueous suspension.The crystals form a repository in the muscle following injection, where they slowly dissolve over time. Injections of testosterone isobutyrate may require a large needle (21 gauge), and may result in local irritation, pain, and redness.
Testosterone Isobutyrate Administration (Men)
To treat androgen insufficiency, testosterone isobutyrate suspension is usually administered in a dose of 50-100 mg every 14 days. When used for muscle-building purposes, testosterone isobutyrate suspension is often administered at a dose of 200-400 mg (4-8ml) per week. Although active for longer periods of time, weekly injections would be preferred due to the low dosage and tendency for pain at the site of injection (large injection volumes would not be advised). To reduce injection volume, the weekly dosage may be further subdivided into smaller injections, which are taken every 2nd or 3rd day. Cycles are generally between 6 and 12 weeks in length. This level is sufficient to provide noticeable gains in muscle size and strength. Testosterone drugs are ultimately very versatile, and can be combined with many other anabolic/androgenic steroids depending on the desired effect.
Testosterone Isobutyrate Administration (Women)
Testosterone isobutyrate suspension is not commonly used with women in clinical medicine. When applied, it is usually given in a dose of 25-50 mg every 14 days. Testosterone isobutyrate suspension is not recommended for women for physique- or performanceenhancing purposes due to its strong androgenic nature, tendency to produce virilizing side effects, and slow acting characteristics (making blood levels difficult to control).
Testosterone Isobutyrate Availability
Pharmaceutical preparations containing testosterone isobutyrate are rare. The only known product at this time is Agovirin Depot, produced in the Slovak Republic by Biotika. It contains 50 mg per 2 mL ampule; 5 packaged per box.
Anabolic Steroid Guide reference
testosterone compound which is used in power sports circles is
Testosterone suspension. In the following we will describe the testerone
dissolved in water. For athletes who readily and frequently work with
the popular oily testosterone suspensions (Sustanon 250 or Testosterone
Depot) this information might be something new. Besides, water-dissolved
testosterone was actually the first injectable steroid. In Europe
during the 1940's injectable testosterone was used in the German armed
forces to increase aggressiveness and stamina, and also in the recovery
of undernourished prisoners of war. This was nothing else but
crystalline testosterone mixed with water. Russian weightlifters began
experimenting with this testosterone compound during the late 1940's
and broke one world record after another. Since, at the time, pure
testosterone without additional esters was used, the substance remained
in the body for only a few hours requiring daily injections, and often
several per day. By first injecting the testosterone molecules with an
ester, such as for example isobutyrate (in Agovirin), it was possible to
prolong the duration of effect up to about one week.
is dissolved in water the substance reaches the blood after only 1-2
hours so that it is unnecessary to wait longer for results, a
circumstance that is advantageous to powerlifters. In the last one or
two weeks before a competition testosterone suspension is injected
daily, often resulting in amazing strength gains. Often Testo
-suspension is even injected on the day of competition to increase the
athlete's aggressiveness and self-esteem in order to approach the
difficult tasks with the right attitude. For this purpose, this rapidly
effective testosterone is considerably more effective than
methyltestosterone (see chapter "Methyltestosterone"). Among East
European powerlifters and competing bodybuilders Testosuspension has
always been a "last minute secret." Especially women can reliably change
their estrogen/testosterone ratio to break down excessive water and to
give softer muscles a visibly better hardness in a short time. Female
bodybuilders usually have considerably greater difficulty in getting
their calves and upper thighs in contest condition than their upper
bodies. Often you see a female bodybuilder on the posing platform with
striated pecs, delts and triceps, whereas her lower body appears flat
and soft. For several reasons the estrogen level can be too high,
leading to an increase in the hormone aldosterone. Since aldosterone
regulates the body's own water household-meaning the higher the
aldosterone level, the more water is stored by the organism it is
important to keep the aldosterone level as low as possible. Finally it
is known that women by nature store fat and water mostly in their upper
thighs. An optimal form for a competition requires a high androgen
level with a minimal estrogen level. Women who on the day of competition
never obtain the right muscle hardness can usually achieve a
significant performance enhancement by injecting 25-50 mg Testosterone
suspension daily during the last 1-4 days before the competition.
However, men also use Testosterone suspension during the last 10-14 days
before a bodybuilding competition to make an all-out effort for optimal
muscle hardness. Athletes report outstanding results when Testo
-suspension is used together with the carbohydrate/loading technique.
The athlete unloads his body by depriving it of carbohydrates for
several days and begins loading carbohydrates three days before a
competition with the goal of storing as much glycogen in the muscle
cells as possible. He can optimize this process by taking 5 0-100 mg
Testosterone suspension/day. Testosterone suspension considerably boosts
the storing of glycogen in the muscle cells and, since dissolved in
water, becomes effective almost immediately. As is known, glycogen also
bonds with water in the muscle cells, which manifests itself in
extremely tight and full muscles.
In the mass-gaining phase Testosterone
suspension is only rarely used. With respect to strength and muscle
mass the gains, as with all injectable testosterone esters, are very
good; however, this testosterone compound requires frequent injections
in order to reach a performance enhancing dosage. With 100 mg every 1-2
days rapid muscle gains can usually be obtained and the strength
increase can usually be felt from the first day. However a stale effect
remains since the injection of testosterone dissolved in water is not
only extremely unpleasant but the pain at the injection area remains for
some time. To endure such martyrdom for several weeks is not to
everyone's liking. The gains disappear rapidly after use of the compound
As for side effects, the same is true for Testosterone
suspension as it is for other testosterone esters. A considerable part
of the compound is converted into dihydrotestosterone in the body so
that acne and hair loss occur quite frequently. The endogenous
testosterone production is already considerably lower after only a few
days of use which during a several week long intake could result in
testicular atrophy and temporary impotence. Women experience the usual
virilization symptoms. An enormously increased sexual drive in both
sexes is noted, often from the first day of intake. The same can be said
about the influence of Testo suspensions on the aggression potential.
Men are also at risk to develop a prostate condition or possible
The price on the black market for a 2 ml ampule, according to reports by athletes, is around $6 - 10. Since steroid molecules do not easily bond with water, Testosterone suspension must be well shaken before the injection. Those who let the injection rest for more than 30 minutes without touching it will notice that the testosterone separates from the watery solution in form of a white, crystalline powder. After shaking, an opaque, white mixture is formed in the ampule.
Wlliam Llewellyn (2011) - Anabolics
Anabolic Steroid Guide