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"Plasma testosterone concentrations were most rapidly and completely suppressed within the first week after injections of the phenylpropionate ester, but this suppression was sustained for the shortest time. The duration of suppression was significantly longest after the gluteal 1-ml injection. Plasma testosterone concentrations returned to base line by day 13 after the phenylpropionate ester but required >20 days to return to base-line levels after the decanoate ester." Minto CF, Howe C, Wishart S, Conway AJ, Handelsman DJ. Pharmacokinetics and pharmacodynamics of nandrolone esters in oil vehicle: effects of ester, injection site and injection volume. J Pharmacol Exp Ther. 1997 Apr;281(1):93-102.
- FSH suppression occurred rapidly (day 3 or 4) but returned to base-line practically immediately after phenylpropionate (IM gluteal) and after about a week with decanoate (Table 6, Inhibin, p. 100)
But nandrolone (as hexyloxyphenylpropionate; Anadur) at 200 mg every 21 days was unable to maintain suppression of spermatogenesis whereas 100 mg testoterone (as enanthate) was able. Behre, H. M., Kliesch, S., Lemcke, B., von Eckardstein, S., & Nieschlag, E. (2001). Suppression of spermatogenesis to azoospermia by combined administration of GnRH antagonist and 19-nortestosterone cannot be maintained by this non-aromatizable androgen alone. Human Reproduction, 16(12), 2570–2577. doi:10.1093/humrep/16.12.2570. Swerdloff, R. S., Bagatell, C. J., Wang, C., Anawalt, B. D., Berman, N., Steiner, B., & Bremner, W. J. (1998). Suppression of Spermatogenesis in Man Induced by Nal-Glu Gonadotropin Releasing Hormone Antagonist and Testosterone Enanthate (TE) Is Maintained by TE Alone1. The Journal of Clinical Endocrinology & Metabolism, 83(10), 3527–3533. doi:10.1210/jcem.83.10.5184
LH suppression was mostly reversed by week 6 post-cycle with 250 mg Test Cyp per week versus week 10 post-cycle in 500 mg group.
This is from a 2018 paper titled Population PK/PD Modeling of Testosterone Cypionate in Healthy Male Subjects by Bi, Perry, Ellerby, et al.
In conclusion, if you're just basically worried about which nandrolone ester is going to give you the most grief with recovery of HPG axis functioning, you're simply worried about the wrong thing if you consider testosterone to be a smooth recovery. Deca is worse than NPP in this regard, but even the Anadur (21-day half life) is unable to fully suppress HPG axis functioning at 200 mg every 21 days unlike testosterone enanthate or cypionate at 100 mg every week.