Hormone nerd checking in.
If you're concerned about not having as much 'va-va-voom' as a result of age related decline or low testosterone then I would first suggest asking your doctor for the appropriate blood tests. You need 2-3 samples to be taken around 9-10am as this is when serum (blood) testosterone levels are at their highest. You'll want to know the following:
Total test - the amount you produce, the NHS considers anything above 300ng/dl to be 'normal', but tell an 18 year old that and he'd be within his rights to go "In the prime of my life having the testosterone levels of an 80 year old is normal?".
Free test - this is the amount of test that is not bound up in protein and is free to act on receptor sites around the body...you can for example have high normal total test, but for some reason low free test.
Oestrodiol - This is a measure of how much female hormone you have, you need some of this for joint health, but the biggest contributor in raised oestrodiol in men is excessive body fat - an enzyme called aromatase is produced in fat, this converts testosterone in oestrogen, more fat, more aromatase, more conversion etc.
The body has a number of sensory mechanisms for recognising how much testosterone is available (hypothalamic gonadal axis...brain/bollock relationship), these sensors however can't tell the difference between natural test from the testicles and test that's been injected. They simply recognise that you have 'alot' and the brain sends a signal to down regulate the production of hormones that make the testicles produce testosterone. This is where the 'your balls will shrink' thing comes from, an organ not doing it's job will shrink, a bit like muscle atrophy in bed ridden/paralysed people.
You can counter this while on steroids by injecting something called HCG which stimulates those precursor hormones. You won't get that on the NHS though because few endocrinologists in this country specialise in hormones from a male well being perspective.
Steroids generally as a whole increase the rate of muscle protein synthesis, which is the technical way of saying the increase the rate at which you build muscle/muscle damage is repaired. It's why people can put on muscle without exercising when the right dosages/compounds are used. The issues are that:
Oral steroids are toxic to the liver, so if you like to have a beer or two, it's a no go. This is less of an issue with injections.
Steroids in general can cause some wonkiness with cholesterol as well as increasing red blood cell count and causing water retention (all of which lead to the blood pressure/ heart disease related aspects). A lot of this is mediated by diet and lifestyle management as well as regular blood work.
Steroids have half lives - in the US, the main forms of test used are Cypionate and Enthanate, these require injection ~3-5 days to maintain stable testosterone levels (and avoid mood swings). In the UK the standard was Sustanon which is a blend of 3 types of testosterone that was thought to extend the injection schedule out to every 14 days, in reality from what I've been able to gather people are most satisfied with injection schedules closer to 7-10 days. Nebido (Test Undecanoate) is being introduced which after some loading shots the guidelines stipulate every 12 weeks, but again some anecdotal reporting suggests better levels stability at 8-10 weeks.
You can still have oestrogen conversion activity going on (and it's the oestro specifically that causes the water retention, it's why women tend to bloat/puff up a bit as their hormone levels go all over the place during cycle) - this requires the use of an aromatase inhibitor to manage, good luck getting these on the NHS because it's not in the steriod guidelines/curriculum but it's usually a 1 or 10mg pill of something taken alongside injections or every 3 days.
Cycling off tends to be problematic as you need to 'reboot' that brain/ball connection, so for a period of time you're going to have cratered testosterone levels (and lowered musle protein synthesis hence 'the gains fall off') and it can take weeks/months to restore natural function. Because the testes lay dormant during this time, creation of new sperm cells may also take some time to come back (yes, taking steroids for as much as one twelve week cycle can make you infertile, possibly for life).
Now with the grey/black market/internet of things...what you have to consider that while it is not illegal for you to purchase, you're going to have no idea whether the gear you are buying has been made in a half way decent underground lab, or if it's been mixed in a thai kitchen sink. Almost all steroids are in an oil suspension, if that oil is dirty/carries impurities then you can say hello to cysts and abscesses.
So, by all means, get your levels checked out (you pay towards the NHS so, might as well get the tests out of them) and there are things you can do to improve test levels such as lose body fat, get more good fats in your diet (omega 3s, so salmon, walnuts and almonds), get more magnesium and zinc and vitamin D in, better sleep, cut back on the booze but it really is a case of once you're on steroids, you may as well stay on them.
Not something to jump on without thorough research into present levels, on going supply, administration and management of monitoring and emergency scenarios.
