Does Nandrolone (Deca-Durabolin, an anabolic steroid) increase testosterone levels?

There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.

From the FDA Drug Label

Nandrolone does not increase testosterone levels, it actually suppresses the gonadotropic functions of the pituitary and may exert a direct effect upon the testis [ 1 ].

• The actions of anabolic steroids, such as nandrolone, are similar to those of male sex hormones, but they do not increase testosterone levels.
• Anabolic steroids, including nandrolone, have been reported to cause serious disturbances of growth and sexual development if given to young children [ 1 ].
• The drug labels warn about the virilization effects of anabolic steroids, such as deepening of the voice, hirsutism, acne, and clitorimegaly, which are related to the androgenic properties of these drugs [ 1 ].
• There is no direct information in the drug labels that suggests nandrolone increases testosterone levels, and the suppression of gonadotropic functions and direct effect on the testis indicate that it may actually have the opposite effect [ 1 ].

From the Research

Effects of Nandrolone on Testosterone Levels

• The study 2 found that nandrolone increases testosterone levels at a concentration of 3.9 μM, but returns to basal levels at a concentration of 15.6 μM.
• In contrast, the study 3 demonstrated that moderate to high doses of nandrolone decanoate induced a diminished serum testosterone level.
• The review 4 highlighted the potential therapeutic applications of nandrolone, but did not provide direct evidence on its effects on testosterone levels.
• The study 5 compared the receptor binding properties of nandrolone and testosterone, and found that nandrolone has a relatively strong effect on target tissues devoid of 5 alpha-reductase activity.
• The study 6 found that nandrolone decanoate and resistance exercise affect prostate morphology and hormone receptor interface in adult rats, and that testosterone levels were reduced in adult and aged animals following the different treatments.

Mechanisms of Nandrolone's Effects on Testosterone

• The study 2 found that nandrolone-induced testosterone increment was associated with upregulation of the steroidogenic acute regulatory protein (StAR) and downregulation of 17a-hydroxylase/17,20 lyase (CYP17A1).
• The study 3 found that nandrolone decanoate altered the expression level of the key steroidogenic enzymes involved in testosterone biosynthesis.
• The study 5 found that 5 alpha-reduction increases the affinity of testosterone and decreases the affinity of nandrolone for androgen receptors.

Implications of Nandrolone's Effects on Testosterone

• The study 3 suggested that nandrolone decanoate may be a potential inducer of male infertility and a potential risk factor for low endogenous bioavailable testosterone.
• The study 6 found that nandrolone decanoate and resistance exercise alter the levels of hormone, converting enzymes, and sex steroid receptors and the morphology of the ventral prostate in adult and aged rats.