It really depends on the drug in question, this is really too vague a question in general.
For Opioids, I'll choose to begin with the one that sorta covers the majority of all opioids administered via IV, (although I have found IV-hydromorphone, oxymorphone, oxycodone, and of course heroin / IV-morphine, [since heroin is basically morphine]: diacetylmorphine which just crosses and permeates the BBB (Blood Brain Barrier) much more rapidly as it is a more fat-soluble version, producing noticeably stronger/more potent effects and often a more intense rushing sensation.
The heroin:morphine comparison is very much, in my opinion, relevant to comparing IV amphetamines, and how methamphetamine behaves in comparison to regular d-amphetamine) therefore, it kicks in extremely rapidly, and particularly with high-dose administration, administered rapidly [as is often the case in situations of abuse], it can cause extremely strong local and systemic histamine reactions including the infamous pins and needles, redness and swelling, severe itching, sometimes even hives, blisters, etc, this all can be reduced by using anti-histamines, which are most effective taken orally as directed (and sometimes topically although it should not be applied topically directly on the injection site, which should be kept sterile, but back in the day when I was an IV-drug user, I would apply some topical diphenhydramine mixed with some hydrocortisone with sterile cotton swabs to alleviate severe local effects that you occasionally get with IV-morphine).
(HINT: DO NOT INJECT ANTIHISTAMINES, NO MATTER HOW MUCH OF AN ADDICTION TO THE NEEDLE YOU HAVE IF YOU VALUE YOUR LIMBS)
Oral antihistamines (50mg Diphenhydramine if you can't get generic Atarax (R), but preferrably generic Atarax (R) / Hydroxyzine HCl should be taken at least 30 minutes prior to the administration of high dose IV opioids. Most common antihistamines have a synergistic effect that many users find desirable, I have even come across a few that have peer reviewed medical literature to suggest some potentiation action, however I am unsure of how that mechanism of action works or would work.
However, I know it's been pointed out that it's been reported to enhance the effect of opioids; oral pre-dosing of common antihistamines like Hydroxyzine HCl (My favorite antihistamine, since it has the least side effects, particularly the drying/antichollinergic effects that benedryl possesses, so in my opinion and experience, Hydroxyzine is about as, or just shy of being equipotent with diphenhydramine).
Diphenhydramine HCl of course, Trade name/active ingredient in Benedryl (R) ), one of the most common OTC medications/antihistamines can be acquired without a prescription pretty much anywhere in the United States of America, whereas for some reason, Hydroxyzine HCl (Generic Atarax (R) ) is RX-only for some reason although it is not scheduled despite it seeming to be RX only perhaps only for patent reasons? I really can't figure out why it's [hydroxyzine] not an OTC/over the counter medication in the USA, like benedryl since is not thought to have any abuse potential and has a lot of desirable effects especially valuble to those of us who take opioids to control chronic pain. Hydroxyzine has shown to exhibit some pain-killiing abilities especially in conjunction with opioid therapy, along with sedative, hypnotic, mild anti-psychotic (As pretty much all AH's are, for example, Quetiapine, the active ingredient in the ever-popular atypical antipsychotic trade name Seroquel (R) is an antihistamine, but depending on the dose, (Under 100mg = powerful antihistamine, but over 100mg it's anti-psychotic powers really start to come out, which is why severe cases of mental illness call for doses nearing a gram a day, although usually given in extended release form.
Speaking of antipsychotics and realizing the topic is IV drugs and their speed of onset, I'll say that probably the most commonly used IV antipsychotic is chlorpromazine (Widely known as trade name Thorazine) which belongs to the older class of typical antipsychotics, which tend to exhibit more extrapyramidal effects in some patients vs the newer, atypical antipsychotics. Thorazine is often given via the oral ROA except in non-compliant patients, who are usually subjected to the IV/IM formulations of it, or other commonly IV antipsychotics used in non-compliant or 'agitated' patients include the extremely potent drugs haloperidol (Haldol (R) ), which is in my opinion, probably the most hardcore antipsychotic that exists and definitely the strongest one that should ever be used in humans, although sparingly due to it's extreme potency making it a likely inducer of possibly fatal extrapyramidal effects. There's also Zuclopenthixol (Acuphase (R), Clopixol (R) ) which is popular in many parts of the world but in the USA, haloperidol is much more commonly used as the "go-to, most-hardcore major tranquilizer in use, probably the most-powerful-to-induce-sedation-in-even-the-most-manic/out-of-control/"Crazy" patients. One of the reasons I bring these class of IV-drugs up anyways is because even though in my opinion, you'd have to be crazy to enjoy abusing antipsychotics but whatever floats your boat.... (no puns intended re: having to be crazy to like antipsychotics, really, I just don't know how else to say it), but if you are overdosing on your DOC / drug of choice, often something fiendish; much more likely to be abused with increased and ongoing or steady deterioration of the ability to self regulate/control redosing like what happens all the time with IV-cocaine or IV-amphetamine abuse. Particularly the former, but the latter as well, are well-known for their ability to land you in the hospital under a 72h psychiatric hold, handcuffed to the hospital bed. Cocaine and (meth)amphetamine psychosis are extremely difficult to treat since patients are so volatile, and everyone's body chemistry is unique and react differently to different medications.
Other IV-drugs used when treating stimulant overdoses are of course, the IV-version of benzodiazepines, which are usually the first line of treatment for managing agitation and anxiety, and hopefully hypnotic effects, but it's often very difficult to sleep when overdosing on cocaine or methamphetamine, regardless of whether your getting IV-benzodiazepines or not.
Common IV benzodiazepines include: Midazolam Hydrochloride (HCl is the most common form although I've heard of others, like midazolam maleate) which goes by the trade name Versed here in the United States, and it's usually only used in surgery, but can be RX'd (although in the USA it is RX'd as the 118mL bottles of the oral/liquid solution which can be used via the sublingual and buccal routes as well as others, not in tablet form like the trade name Dormicum (R) tablets of Midazolam that are on the market outside of the USA. Besides Midazolam, which is extremely short acting which makes it unfit for management of most conditions, as one with experience with insomnia and hypnotic medication might imagine, a drug with so short a half life with such high potency often leads to rebound insomnia and IMO, is a drug that you honestly want to only use in hospitals. Abusing midazolam can have drastic consequences, which I liken to abuse of fentanyl: If you get seriously injured, these are the first-line / go-to drugs used by anesthesiologists / doctors in the field to manage your pain, and they will freak the fuck out if an obsecene dosage of midazolam doesn't control your seizures or an unspeakable amount of fentanyl is required to manage your pain during a procedure and you did not tell the doctors about your tolerance to the medications. Trust me, if you have the option of receiving effective usage of the regular cocktail they give you in hospital as anesthesia, which is most commonly going to be fentanyl citrate / midazolam HCl, two super short acting drugs to control your pain and cognitive function respectively during a surgery, it's going to be a helluva lot better than making them guess your tolerance after they've knocked you out. If you haven't heard of anesthesia awareness, which is basically when you've been paralyzed and cannot express distress, but you are not receiving adequate pain or amnesic relief, well that's supposed to be one of the most traumatizing experiences out there, understandably so, which brings us to the moral of the story: If you're an IV drug addict, and are likely abusing a class of medication (opioids) you might need to control acute pain one day, God forbid, you are fucking yourself over by having such a high tolerance to IV pain medication, your going to be shit out of luck if you ever sustain lasting injuries and suffer chronic pain becoming completely and utterly reliant and dependent on the drugs you once abused (hey, this sounds just like me!) you'll be shit out of luck. So those of you [still] reading this, considering whether IV drug abuse is the right path for you, I sincerely hope that you if at the very least choose to continue down that road with no destination, that highway to hell, I really do hope you ask yourself first, and with every shot, "Is it worth it?" I guarantee you that while the addict inside you may scream YES, YES, ANYTHING FOR THAT SWEET RELEASE, the rational part of your soul that has yet to be touched by drug addiction and is not influenced or biased by the experience of the rush of a shot of Dilaudid (R), which contains the desired ingredient hydromorphone HCl: one of the most water-soluble, most-often-abused-via-the-IV-ROA, opioid narcotic, as it is about 4-6x stronger than morphine when injected allowing for a lower dose to produce more analgesia.
It [hydromorphone] is more lipid soluble than morphine sulphate and due to it's semi-synthetic nature, / being scientifically tweaked by mankind for a more optimum/desired pharmacological profile unlike the natural opiate alkaloids, morphine being the former "gold standard" treatment for acute pain.
morphine- present in the Opium Poppy in raw form, exhibiting more side effects than the semi-synthetic class of opioids, which are:
-not found in the opium poppy but can be found as metabolites in the thebaine-derived opioids
-significantly tolerated better / more bearable for most patients in comparison with traditional IV-morphine, which is notorious and infamous for it's rapid mechanism of onset and the significant histamine response seen both locally and systemically as I discussed in the opening paragraph, all of this is what is making hydromorphone the rapidly increasing default choice as the, well, default..../ go-to "gold standard opioid" & first desired line of treatment by prescribing physicians in the hospital setting.
Dilaudid is IV'd a ton, so is it's chemical cousin, Opana/Numorphan (Oxymorphone Hydrochloride, which is probably the strongest full-agonist opioid narcotic in demand on the market in the USA, [besides the Bentley compounds / fentanyl analogues], definitely stronger than heroin IMO/IME.
When you're injecting it, (or even snorting really) oxymorphone hcl is perhaps one of the easiest drugs to overdose on accidentally, and it certainly ranks #1 as the most addictive opioid I've tried by a long-shot. It's got "surprisingly" violent and unforgiving withdrawals, I would relate it very closely to the sensation of fentanyl withdrawals, like the one chronic pain patients experience when an old patch wears off and the new one does not kick in in time, causing horrible rebound pain and violent withdrawal symptoms leading to heavy use of breakthrough medication during this time period due to incorrectly managed pain, something that one should speak to their doctor about immediately if they are experiencing.
As I think over the most commonly injected drugs, I cannot forget IV-methamphetamine: from the taste it leaves in your mouth after pushing off, to the inevitable cough and oblivion that accompanies IV administration of crystal methamphetamine, it is ALL BAD NEWS. Not worth it. None of these drugs are worth putting a needle in your arm. That is my official and unofficial stance on IV drug abuse, not a single one of these drugs is capable of producing desirable effects that are worth it in the long-run, and most of them fail to do so in the short-run, which leads many of us to chase that ghost and then your mild experimentation becomes full blown rationalizing drug addiction. Pretty much all of the drugs that my close friends inject, in my honest-to-God opinion, are not at all worth the fact that you're putting a needle in your arm (or wherever injection site you force yourself to use), bypassing ALL of your bodies self-defense mechanisms against foreign invaders/threats/diseases/bacteria/viruses/fungi/etc. Your chances of contracting a bloodborne disease are much higher as an IV drug addict, so it is critical to regularly get tested for things such as Hepatitis or MRSA (Medically Resistant Staphylococcus Aureus infection which can be fatal if it spreads to critical areas such as your heart valves, or lead to loss of limb, life, liberties and physical abilities you once possessed) and this is why it is CRITICAL for you to maintain a STERILE injection process if you absolutely cannot be persuaded against using the IV-ROA, ignoring all logic and reason / despite the many ways that you can achieve desired effects without putting a needle in your arm, you MUST be responsible and take steps to lessen your the likelihood/chances of death or worse: these odds, which are stacked against you, are your responsibility to try and overcome and in the process of doing so, being extremely careful that your drug abuse does not infringe the rights of others to pursue life (and good health), liberty (Prison- likely this is where you go if you get caught up, and it is a horrible environment to detox in, pretty much the opposite of rehabilitation...)
So yeah, IV drugs, kick in real fast man, how many seconds? Depends on the drug. Methamphetamine kicks in just as fast when taken via the rectal ROA in my experience, so I never think of injecting it (nor do / will I ever again choose to inject any drugs unless directed to do so by a doctor, and even then I'd have to exhaust every other option before accepting the needle as a part of my day again.) Morphine rectally takes a lot longer and is nowhere near the parade and fireworks it alludes to be when injected straight into the vein, but I don't mind waiting the extra 30 minutes for it to kick in, especially since it still produces a rush for me via the rectal ROA, and it's analgesic potential via the rectal ROA is substantially higher than other ROA's for my unique body chemistry. I recently got almost a full 72h of strong analgesia from a mere two! rectal shots of morphine, I noticed significant reduction in my levels of pain upon awakening the next day, and even the day after that, I had still not returned to baseline and I was displaying all the signs of analgesia, which was still going strong at the day 2 mark, lasting significantly over 24 hours and was on par with the level of analgesia I'd get from wearing a fentanyl patch, minus all of the side effects that I tend to experience with fentanyl transedermal patches (Like sensations of impending doom/overdose. Patches are something that I sincerely hope none of you are injecting, if that's not the end of the road, I don't know what is.... There is no safe way to abuse fentanyl patches).
Please be safe, and think twice before even thinking of abusing the IV-ROA. It may seem to be "the best" to some people, but there are a ton of reasons why you shouldn't IV drugs, despite the IV-ROA tending to have the lonely pro of possessing (usually) the ability to become completely absorbed by your body, adding stress to your liver, circulatory, respiratory, and immune system(s) in the process, just so that "nothing is wasted?" (except arguably undeniably, your health- physical and psychological)????
Is it worth it? Fuck no. It is the Song of the Sirens, and if you answer the call, everything you thought was true, everything you took for granted, will be taken from you piece by piece; your ship is destined to crash and burn at the spikey stakes that await you, ever patiently, at rock bottom. Thankyou for listening, I hope just one of you reading this reconsiders putting a needle in their arm for the first time for whatever stupid reason you've been told.
Friends don't encourage friends or fellow dope fiends to shoot up, ever, for any reason. Be strong and make better choices.
