Answers to your questions. I have extensively (over 2 years) used L-carnitine injectible, kynoselen and B12, together and separately:
L-Carnitine
Painful? A little soreness for a day after injection
Effective? Ok, but not that dramatic. Helps with fat metabolism, but not a panacea.
At what dose? 400mg EOD injected
For how long? Months
Sides? Nothing noticeable
Kynoselen
Painful? Yes, and some knotting. Site soreness for a day or 2 after injection
Effective? Ok, but again not that dramatic. Works by upping AMP levels, makes me sweat more during workouts and train a little more intensely (although that maybe in my head)
At what dose? 2ml ED or EOD injected
For how long? Until I use up a 100ml bottle
B-12
Painful? Very little soreness at injection site, pretty painless
Effective? Ok, but not that dramatic. I don't feel much energy or appetite increase, although some others do.
At what dose? 2000mcg EOD injected
For how long? Months
Sides? Nothing noticeable
That's been my experience.
DrG