Hi, I am new to posting here and I have tried very hard to make sure that this question has not already been addressed but I cannot find it discussed anywhere. If it is already covered please forgive me.

My questions are:

Can an Apothecary use the medicae skill to treat himself with the 'first aid' special use?

If yes, then can he also benefit from his own Narthecium while doing so?

Can an Apothecary use the medicae skill to treat himself with the 'extended care' special use?

If at all possible, references for your answers, if they exist, would be appreciated.

Thanks a lot for your help!

You certainly can - at least I can't find any suggestion to the contrary in any of the relevant descriptions. The same thing makes it hard to provide references: there's no rule explicitly stating you can , it just doesn't say you can't. That also means all skill check modifiers apply, including the bonus provided by Narthecium. Lore also supports this, as Apothecaries rarely do major surgery on the field - enhancing the healing abilities of the Battle-Brothers bodies or stabilise their state when damage overwhelms said abilities is usually the best they can do healing-wise.

Of course, there are also some extreme cases where common sense has to apply. I obviously wouldn't allow an Apothecary overseeing his own recovery while in a sus-an healing coma, and I'd only let an Apothecary tend to himself in cases of, say, multiple limb loss, when in a fully kitted-out facility, with available medical assistants or servitors present. Such cases aside, however, he can just as freely insert himself with hormone cocktails or sus-an coma-inducing drugs and apply bandages as he would with anybody else.

If the books don't specify anywhere then apply the rule of common sense.

Using medicae on yourself, yes, easily. If you know first aid for example, say you have a nasty cut from a thug trying to mug you then, as long as you are conscious and able to comprehend what you are doing and not dead then what's stopping you from applying said medical knowledge to yourself? Keep pressure on it, staunch the bleeding etc and make sure its clean of infection.* Saying you can't would be condemning yourself to death and having all your blood go bye bye just because the nearest other doctor is in the next city across?

Now of course for a marine there's more to it than just fixing a flesh wound like a huge gash and we're talking missing limbs or bolter holes. Arguably though the principle is the same, stop bleeding, make sure it's clear, bandage/seal it up and move on. To say so otherwise would be utter absurdity. If you are arguing this with a player or GM (which is why I theorise you're after references) clout them and tell them to apply reasoning!

With extended care, same again. As long as you are conscious and aware of what's going on then theres no reason why you can't administer your own care process or shout at a scrub to do it:

"You, useless medical servitor. Get over here. Get me some vicodin, fresh bandages and a cup of tea. I've prescribed it for myself."

As long as you are physically capable of doing it or getting someone else to do it for you with specific instructions and guidance, then I don't see why not.

*I would like to point out I do NOT have medical training and there's probably more to it than this and is only intended as a proof of concept. I am not held responsible for any deaths caused by my poor medical advice and trying to cure injuries caused by chainsword related accidents.

"You, useless medical servitor. Oh wait, you're the assistant. You, useless assistant. Get over here. Get me some vicodin, fresh band-aids and a crate of whisky. Hold on. Make it two crates, and that freaky stuff you got me last time. It's all right. I've prescribed it for myself."

Here, FTFY

"You, useless medical servitor. Oh wait, you're the assistant. You, useless assistant. Get over here. Get me some vicodin, fresh band-aids and a crate of whisky. Hold on. Make it two crates, and that freaky stuff you got me last time. It's all right. I've prescribed it for myself."

Here, FTFY

Tea fixes everything. The Imperium is effectively the Space British Empire ergo it's all about the tea. Or as this universe calls it, recaf!

Looks like you're mixing up the preferences of the Imperium with the preferences of Ciaphas Cain, which is a forgiveable sin Remember though that he himself preferred to drink tanna when he (or rather Jurgen) could get his hand on it.

I also have to admit that I'm a bit intrigued. What else besides a taste for tea could characterise a retelling of the Imperium of Man as British Empire... IN SPAAAACE?

Furthermore, I maaaay have watched too much Archer and Frisky Dingo recently, causing a bit of a popcultural cross-contagion, as evident from my post above. Nonetheless, I still like the idea of an alcoholic, overconfident, Rick-of-Rick-and-Morty-crossed-with-Archer type Apothecary.

Looks like you're mixing up the preferences of the Imperium with the preferences of Ciaphas Cain, which is a forgiveable sin Remember though that he himself preferred to drink tanna when he (or rather Jurgen) could get his hand on it.

I also have to admit that I'm a bit intrigued. What else besides a taste for tea could characterise a retelling of the Imperium of Man as British Empire... IN SPAAAACE?

Furthermore, I maaaay have watched too much Archer and Frisky Dingo recently, causing a bit of a popcultural cross-contagion, as evident from my post above. Nonetheless, I still like the idea of an alcoholic, overconfident, Rick-of-Rick-and-Morty-crossed-with-Archer type Apothecary.

We all know the Golden Throne is actually based in Nottingham...if it still existed by then!