Testosterone killing your immune system

I have no idea about TRT and immune system but what you wrote makes me wonder if "never catching even a cold while on opiates" has something to do with their effects on testosterone too.
Can’t speak to heroin but I can tell you that after 20 years of pharmaceutical opioids (at high levels), there’s no such thing as not getting a cold while on opiates. You get sick no more or no less regardless of how many oxy 80’s ER or oxy 30’s IR you take. Or Dilaudid, or Vicodin, or Morphine, or Fentanyl patches, or whatever. Old wive’s tale.
 
High testosterone does have an effect on the immune system. Same as it's related to higher rates of heart problems, high blood pressure etc.
For women, oestrogen does have a protective factor concerning general disease, but on the other hand it is linked to significantly greater susceptibility to developing autoimmune conditions.

It's kinda the evolutionary trade-off for greater physical strength in men (useful if you have to fight other men) and greater resistance to common infections in women (which is obviously good to have if you're the one carrying offspring).
 
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