When on TRT your testicles will lose efficacy and size over time. It is 100% guaranteed. If someone has been on TRT or using steroids for a very long time, HCG and HMG can still bump your LH/FSH/sperm count/testosterone levels for awhile, and generally HCG/HMG will do a good enough job to allow you to conceive. However, after many years of TRT the likelihood of halting the use of testosterone and recovering to good natural levels are slim. It is just a trade-off we take. However, if someone is on TRT their natural production should already be poor to begin with. Using HCG (10-15k units twice a year) will most definitely help slow down the process of testicular atrophy though, which is why I do it.
I had a serious opioid addiction for years as well. I do not believe, from my understanding, that opioids cause testicular atrophy. Opioids simply reduce your testosterone levels when you are using them for long periods of time, but when opioid use is ceased, your levels should return over time.
Personally, I would not do 5,000 units in one shot. The most HCG I feel comfortable using is 2,500 units EOD. I think at 5,000 units in a day you could potentially cause damage to your leydig cells for no real additional benefits.
Many doctors seem to like putting guys on HCG FULL-TIME at 250-500iu per week. I do not really understand this. There are no solid peer-reviewed studies (that I know of) that support the use of HCG full-time at 250-500iu per week while on TRT. If one exists, please send it my way. It is just not enough HCG, IMO. Your HPTA is a feedback loop. If your pituitary and hypothalamus are sending a signal telling your testes to shut off and produce zero testosterone because you have exogenous testosterone being introduced weekly, then you will need a very strong opposing signal in order for your body to kick natural production back on. 250-500 units of HCG per week does NOT provide a strong enough signal to overpower the signal from 200mg of testosterone. That is a simple explanation.
You can dose your HCG in a thousand different ways. If I am going to use 15,000 units I will usually do something like this: 1,500iu EOD for two weeks, and then 750 units EOD for two weeks. Before doing this, I will also lower my TRT dose to 100mg/wk for 6 weeks or so to slightly lessen the shut-down signal strength from my pituitary to my testes. Lowering my testosterone like that is not a proven scientific action, it is just something I do based on anecdotal experience. Bryan Moskow, "The Guerrilla Chemist" has a similar HCG protocol that you could look into. It has the same idea; higher dosing for a week or two, and then successively reducing the dose every week until you stop.