Promethazine is nasty trash. Its a sedating antihistamine. but also a phenothiazine antipsychotic dopamine D2 receptor antagonist. Thorazine's little brother, weak antipsychotic of the 'typical' class and will shit all over euphoria, also it interacts with CYP-P450 hepatic enzyme pathways afaik, as well as being an antimuscarinic.
Generally pretty nasty shit, definitely NOT conducive to euphoria. I'd just take the codeine and ANY other sedating antihistamine if your going for a combination of codeine/sedating antihistamine. Take the codeine, all the dose, first, then allow it to come to just before the peak, with sufficient time to co-incide the peak of both ideally, but don't use promethazine, its trash, its counter-euphoric, its got potentially really awful side effects like akathisia, tardive dyskinesia (can be permanent), and the akathisia itself is awful if it happens, I've had other drugs cause it and its one of the worst things you vould possibly have happen to you in terms of making you suffer. Akathisia will make you beg for death)
Do NOT inject codeine sham, its a prodrug for one, needs to undergo first-pass in the liver, which IV bypasses, before it turns to active substances such as morphine and various glucuronide conjugates, and injecting codeine can cause massive histamine release, sufficient to cause pulmonary oedema (medical term translation-blood plasma pours out of blood vessels rendered more permeable by the histamine release and other such proinflammatory mediators being released and fills the lungs, so you drown in your own blood plasma, as your inflamed lungs fill with fluid and you slowly drown on dry land, unable to breathe)
Also not everybody can either get H, or turn codeine to morphine and react morphine with a suitable acylating reagent. AFAIK dihydromorphine from dihydrocodeine is easier, using concentrated anhydrous hydrogen bromide gas in glacial acetic acid solution, in a pressure 'bomb' heating vessel for conducting reactions under combined heat and pressure. Don't know if this works on codeine, would think more people would be doing so if it did, but DHC can be made selectively into DHM, by this method, apparently under these conditions, surprisingly indeed, and somebody did this, verified it via GC-MS, to find it selectively demethylated the 6-position methyl ether, giving dihydromorphine. I've actually had a dose of that very product too, after its being acetylated, to form 6-monoacetoxydihydromorphine and my fucking christing god on a hotdog bun! I've never had a hit like that before..not even from dipropionylmorphine. Rush for 3/4 hour or so, after (note-highly tolerant, without a hefty tolerance, the dose taken would have felled me I'm pretty sure of it) from 300mg 6-monoacetyl-dihydromorphine IV, and despite being able to slam a gram of dipropionylmorphine, morphine or non-street heroin, that...the 6-AcO-DHM? that had me staggering like I'd just took a hit from an antitank rocket from just feet away, and somehow stayed alive, but knocked senseless. Fucking christ, it was that intense. Mental, mental, fucking euphoric as hell shit.
Seriously though screw the promethazine. If you can still get 'valoid' tabs otc, cyclizine, go for that for the antihistamine, plugged in solution (suspension of ground tablets), it acts very quickly that way and has a big reputation for potentiating opioids. I get it on rx for GI distress and cyclizine is amazing for antisickness effects too. If its to be injected however the hydrochloride form isn't adequately soluble enough and needs to be basified, extracted into a nonpolar solvent of choice and from there, treated with a dilute organic acid such as ideally, lactic acid to form the very soluble cyclizine lactate, which is the form used for IV preparations. Alternatively, I should think that the citrate or ascorbate (vitamin C salt) would probably work well too. If it can't be done by a given person, then plugging the cyclizine is the best way to do it, if someone doesn't want to or cannot (for heroin not codeine, which as stated should never be injected) or with morphine etc. or other IVable opiates, then plugging a slurry of the HCl tabs ground up will substitute although not be quite the same as combining the two in the same rig.
Be aware that it does have anticholinergic effects, so don't take too much.
If anybody wants, I can test the solubility of the citrate, and/or get some ascorbic acid (vit.C) and prepare some cyclizine citrate or ascorbate and measure its solubility, got plenty cyclizine alright.
Although if I may be excused, people, LC has some other chemistry work to attend to and something to recrystallize and purify to get up to standard as it ought to be, along, maybe, with a vacuum distillation of something else. I am a busy man, and one who A-cannot sleep right now, unless he were to take a dose of nitrazepam perhaps, so instead, since he's used it two days in a row, in one week he'll occupy himself recrystallizing some samples, vacuum-stripping solvent out of something, distilling some anhydrous ethanol over quicklime whilst protected by a dessicant packed drying tube for use in cleaning a certain sulfonic acid which needs purification. Another of those late-night sleepless projects, that tend to happen in one form or another when LC can't sleep. He's not one to toss and turn pointlessly when he knows he won't sleep, rather he prefers to use the time to dive into the o-chem, and various bits and piece of inorganic, and metallurgy (fr.ex one of his last inorganic projects was turning 'water glass' first into acid-precipitated very fine silica dust, cleaning out the salts and residual sulfuric acid, and then using a pyrometallurgical reduction of the magnesiothermic or aluminothermic type, Mg IIRC was the one chosen due to relative ease of dissolving the slag after, out of the crucible, to reveal some nuggets of pure elemental silicon. Well when he says pure, he means on a chemistry-level rather than semiconductor grade of course, he doesn't NEED that level of ultra-high purity, he isn't making integrated circuit wafers etc.
Although he WOULD love his own semiconductor chip/wafer fabrication setup so he could grow his own semiconductor laser or more interesting yet, quantum-well SASER wafers that can be electrically pumped. (a SASER, or sono-accoustic 'laser' is basically the sound equivalent of a laser, generating beams of highly coherent sound, the sonic equivalent of a laser, although the physics are different, and as LC understands it, don't involve a population-inversion like lasers do. Or other intriguing ideas like exciton-polaritonic lasing, polariton lasers apparently being extremely efficient in conversion of energy input to output. Always wanted to build both. Although the SASER, using non-semiconductor gain media is likely more within reach than a DIY polariton laser.)
And here, taken out of its bottle that it usually lives in, is the resulting silicon, originally made from silicate solution and concentrated sulfuric acid, before washing out the potassium sulfate and the residual H2SO4, its the little shiny nuggets of what looks to be a metal, in the palm of a hand, in between the container marked 'dichromate' on the far right, the bottles of acid halides and alkyl halides, acyl anhydrides at the back, and the jar of metal on the far left inside a bag within the jar, above a mixture of shiny metal powder and dull whitish stuff (a mixture of magnesium dust, and anhydrous calcium chloride, for the metal in the jar is elemental lithium, protected by purging the jar with dry argon gas, and a mixture of CaCl2 to absorb water whilst the magnesium dust serves as a sacrificial oxygen absorbent and over time, scrubs any oxygen that might manage to make it in and attack the lithium, since there is no oil on the Li, and in fact my method of preserving it this way, even after opening the inner bag that I received my Li metal in, has actually not oxidized and degraded in any visually significant way since I bought it, and that must have been a year ago at least. Preserved better than my sodium metal brick, which arrived in a vacuum-evacuated, heat-sealed, wrapper, covered inside in a layer of paraffin oil of some kind, hermetically sealed within an outer bag of inert gas. Its actually in better condition, having been opened and some used more than once, than my block of Na, which does have some oxidation present on it, although not much%)