Speaking of Deca causing thyroid issues, this is from the study:
Methods: Male Winstar rats were treated with vehicle or 1 mg·100 g-1body weight (b.w.) of DECA, once a week for 8 wk, intramuscularly.
1 mg / 100g is also 10mg / kg. We need the dosing in kilogram to convert it later.
To find out what that is in Human Equivalent Dose (HED), we need to use a conversion chart and formula:
Human Equivalent Dose (HED in mg/kg) = Animal Dose (mg/kg) × Animal Km ÷ Human Km , where Km is a correction factor reflecting the relationship between body weight and body surface area.
For a typical adult (body weight 60 kg, body surface area 1.6 m2), Km is 37.
For the most often used laboratory animal species the average Km are as follows:
Mouse 3
Rat 6
Guinea Pig 8
Rabbit 12
Dog 20
Human Adult 37
The problem is the FDA is using an outdated system...and by outdated, I mean they are using one devised in 1883 and superceeded in 1932. Go Go US Government for being up with the times! Anyway, I am going to use the correct formula instead of the one from the 1800s. We will use the alternate determination method instead of the incorrect simplified one, mostly because the simplified one is not to be used for intramuscular dosing...and it is just plain wrong. The better formula is:
HED = animal dose in mg/kg x (animal weight in kg/human weight in kg) ^0.33."
The correct scaling can be determined using the formula the FDA provided but with the correct exponent of 0.25 (instead of 0.33) and assuming a 90 kg (200 lb) human and a 0.25kg rat (weight of the rats used in the study). Plugging in the numbers, we get:
10mg/kg X (0.25 kg/90kg)^0.25 = 10mg/kg X 0.2395 = 2.4 mg/kg.
Then we take that number and multiply it by 90kg to find the dose needed to meet the requirements of the study:
2.4 mg/kg X 90kg = 216 mg per week (the rats were given their dosing weekly). From the study:
The animals were divided into two groups: normal control rats (submitted to vehicle injection; peanut oil with 10% of benzoic alcohol) and rats treated with nandrolone decanoate (Deca Durabolin (50 mg·mL***8722;1 Organon)) 1 mg·100 g***8722;1 b.w. Steroid and vehicle were administered by a single intramuscular injection in the hind limb once a week for 8 wk. The dose used was 60 times higher than the dose usually recommended for hypogonadism in humans, but corresponds to the dose generally used by anabolic steroids abusers. After the experimental period, the animals were decapitated and blood was collected for hormone concentration analyses
So there you have it, the study shows that if you are using over 200 mg of Deca a week, for 8 weeks or longer, you have a risk of lower T3 and T4 (collectively called TSH) levels in the body, as well as lower testosterone levels due to the testes shutting down from the Deca. They are not sure if the problem is from Deca directly or from the shutdown of the Testes. Why does this matter? Well, according to the study, previous studies were done on humans who admit to using Deca:
The reports of serum TSH changes found in AAS abusers are controversial. A previous study in athletes who used AAS also found a reduction in serum TSH levels. Increased serum TSH, however, has been described in individuals submitted to a short-term treatment with AAS, whereas in weightlifters who used AAS no significant difference in TSH levels were found
What is one of the biggest differences between weightlifters and what most people think of when they think of an athlete? Muscles - and lots of them. What is the one drug weightlifters say to NEVER skimp on when running anything at all? Testosterone. In fact, their study even mentions that testosterone promotes the creation of the cells (thyroid) that create TSH in the body:
Reinforcing the possibility of a direct action of androgens on thyrocytes, Banu et al. demonstrated that testosterone induces thyroid cell proliferation in cultures.
My takeaway, as a layman, is if you want to be the safest possible while still using deca is to use 200mg or less of deca a week and also make sure to use enough testosterone to at least keep yourself at normal human test levels. It does not talk about supra-physiologic testosterone levels, but it also does not rule them out (and since it is talking about weightlifters, I would say the testosterone levels are probably outside the normal human range). I would also say that using higher levels of deca is fine provided the level of test is also increased - exactly like what is done during bulking.
