What does a 'high opiate user' mean? can you give us a bit of information on what opiates you use and at what dosages, and how you administer them (IV, oral, rectal, intranasal etc.)?
It also depends on the capsule size, but it seems most of them contain either .5g or .6g. For me, when I first started using kratom to get off suboxone, I only had to take 10-15 of the .6g to get a very noticeable effect. I should mention I was taking 2-3mg of suboxone, usually sublingually or plugging. IDK if my receptors are just weird, but I don't find kratom to be a 'weak' substance. Maybe on a mg/mg basis, then yeah, but with kratom the threshold dosages are usually 1-3g's. If you're coming off subs like I was, 7.5-9g's worked perfectly fine for me. For some reason the buprenorphine doesn't seem to block suboxone (at least at those dosages) at all for me. I've heard other people have experienced the same thing. I'm not sure about how mitragyne and other alkaloids in kratom interact with opiate receptors, 7-hydroxymitragynine I read (somewhere 'scholarly', now I can only find posts on BL with no sources to back them up) has a binding affinity of somewhere between 15-34x that of morphine (I got both those numbers from two different posts on BL, maybe someone can find a source for them as I'm having trouble), whereas Buprenorphine has a binding affinity 20-40x that of morphine. I don't know about the other alkaloids, and 7-hydroxymitragynine 4% of what is in kratom, but it may be true that some of the alkaloids in kratom have a binding affinity that is close to or higher than buprenorphine. All I can say is that for me, 9g of kratom most definitely not only takes away my withdrawal symptoms, but it puts me in a good relaxed mood too.
Also, another weird thing I've experienced with kratom. I had been taking it by just putting my dose in a piece of tissue and bombing it, and due to daily use, I obviously started to become tolerant to the point where I basically got no effect from taking the kratom, other than it just taking me out of withdrawal. However, a few days ago I was bored and decided to try making kratom tea, as I thought I might get something more out of that due to the fact that the alkaloids are already extracted and ready to be absorbed, rather than having my stomach break down all that plant matter. To my astonishment, I got a much more potent effect out of making the tea. It's weird because I feel like making the tea must be way more wasteful than bombing it, but I get not only stronger effects, but a different type of effect too.
When I was just consuming the kratom in tissue paper, I more often than not got a more stimulant experience (btw, I've been using Bali), and in higher dosages, just the mildest feelings of relaxation/sedation. Now with the tea, the onset of effects start within 5 minutes, and peak after about 30, and the experience is totally different. There is a feeling of 'stimulation' but it's more along the lines of tradition opioid stimulation (like oxy or something) than say, amphetamine. It's the type of stimulation that were you to sit down and watch a movie, would turn into relaxation. After 30-45 minutes, when I peak, the effects become more sedative/anxiolytic. Since then, I've only been making the tea. I find the best way to 'brew' it, is to let it soak in lemon or lime juice for a good 20 minutes, then bring it to a boil, lower the heat down so that it's simmering, and let it simmer for about 20-30 minutes, then strain it, throw the plant matter back in the pot with some added water, bring that to a simmer, strain it a second time and add the second extraction to the first one. Another interesting thing I read on DF, which was quoted from some scholarly anecdote, was that (the author-who was testing out extraction methods and their efficacy) found that making kratom tea, using the water extraction method, at best yielded only 36% of the active compounds in kratom, and that was after letting it boil for 2 hours.
I imagine that some of the alkaloids are more soluble than others, which would explain for the difference in subjective effects in terms of tea v. bombing, but it still kind of shocked me that only 36% was extracted through water boiling. (The author also found that boiling it for longer did not yield more goods, though boiling it for less time reduced that percentage). It makes me wonder the absorption of the different alkaloids through toss n' wash/bombing as well.
Also, don't smoke kratom. From what I've heard all that will do is give you a head ache, even if you have it in a resin form. Just take it orally, no matter what it has a fast onset, but if you want the fastest, drink the tea. The effects are similar in a way to hydrocodone but it obviously has a more organic feel to it. It's a cool plant, in lower dosages it acts as a stimulant, not as intense as amphetamine, but the effects are definitely closer to amps then to opiates (at low dosages), the higher dosages create an opiate effect.