Yes writer - am an anaesthetist. Although for the purposes of most of the threads I write on I'm just an anxious first time mum!
The painkillers you get put on post section vary somewhat trust to trust (local prescribing policy) but in general are: paracetamol - fine to breast feed with, ibuprofen or voltarol (which is what the suppository you get given at the end of surgery is) - also fine to breast feed - and some kind of opiate. This used to be codeine but there are several drawbacks. Codeine is metabolised to morphine in the body an it's the morphine that actually does the painkilling bit. The degree to which you metabolise it, which is determined genetically, determines how much morphine you get so how well it works as a painkiller. Some people get pretty much no effect, some can be pretty spacey on a fairly small dose. So that's one drawback. With breast feeding, the metabolizes are secreted in breast milk so some mothers end up giving their babies a big dose of morphine which can make them sleepy. There was a case not so long ago (in the states I think) where the baby died from effectively and overdose from opiate in breast milk. There were confounding factors though - from memory the baby had been noted to have been sleepy but nothing much had been done about it, and it's a pretty rare example. So again, we're back to the risk balance thing. For some people, codeine is a great pain killer and fine if you know to keep and eye on your baby and if it seems excessively sleepy then do something about it. For others, it little more than a pants painkiller with constipation side effects.
Oromorph (oral morphine) is usually given for the day or so after the section whilst you're in hospital. Again, can be passed to the baby but again, if it seems sleepy - people around to notice. And it's metabolised much more reliably than codeine. No reports (as far as I'm aware) of neonatal harm.
Naloxone reverses the effect of opioids (including morphine, diamorphine). Diamorphine is heroin, which is why you dh recognised its naloxone response Raxa, but we tend to give tiny doses, esp in a spinal, and not cut it with bleach and inject it with dirty needles!
Most drug manufacturers say avoid in breast feeding, not because they've tested it (ethical nightmare) but because they haven't tested it, don't know and can't afford the litigation if something went wrong. Most drugs used in obstetrics therefore are 'tried by time' i.e. Pregnant women have had them for years without notable consequence. And by the time your baby's born, if it needed a lot of the drugs itself, it'd get them anyway..... Including morphine.