Oral administration works extremely well with 3F-P. I need roughly 50% more substance compared to intravenous use, resulting in an estimated 60% oral BA for me personally.
Due to the significant health hazards I would strongly discourage rectal administration of stimulants!
More information below.
The following are taken from the bioavailability thread and are not double checked. They only list bioavailability, not speed of onset. Afaik there is a correlation between these though. I would have to look up the respective articles for more information on the latter.
Hydromorphone: Oral-30-35%; Intranasal 52.4%; Rectal 33%
Oxymorphone: Intranasal 43%; Orals 10-20%; Rectal 10%
Rectal oxycodone bioavailability is 61% (which is similar to oral at 60-87. There is greater individual variability with rectal (+or-30% range 16.4-126.8 and peak plasma for rectal is a rather lengthy 2.8 hours."
Ketamine is really shitty via this route, both in terms of BA and absorption rate.
DXM gives no effects at all in my experience.
Rectal bioavailability and speed of onset of amphetamine vary significantly between individuals. I have personally had some very disappointing experiences with it.
Additionally, a lot of substances' bioavailability and speed of onset depend on the rectal pH, anatomical properties like the size of the rectal surface area or anastomoses to superior (portal!) rectal veins. Codeine and Morphine are good examples of that, they both get absorbed a lot better in a high pH environment which one cannot rely on finding in their rectum at a given point in time. This is true for many substances which makes rectal administration less reliable than oral or intranasal administration.
I won't get into more substances here, but focus on other issues with the rectal route of administration that make many substances - most importantly stimulants - a very poor choice! Generally speaking, you are correct that rectal administration can be effective for a large number of substances due to lower ratio of portal vs systemic absorption.
For anything that depends on first pass metabolism rectal administration is obviously a bad choice. Examples are Tilidine or Tramadol. Codeine phosphate needs to be demethylated via first past metabolism if I am not mistaken.
I suppose most substances are indeed better absorbed via the rectal roa, but insufflation often rivals or surpasses it. Can't hurt (well it could actually hurt quite a bit ;D) to try plugging 3F-P, but I would personally avoid it due to it's apparent proinflammatory effects on connective tissue, possibly even local vasoconstriction leading to cell death.
Aaaaand, who would've guessed it, I found out this is true for other stimulants as well after reading up on it! I was actually spot-on correct:
The application of methamphetamine directly to rectal mucosa likely has local vasoconstrictive effects, making rectal ischemia and necrosis a potential complication.
With 3F-P I would therefore be even more careful about administering it rectally! In the name of harm reduction it is a dangerous recommendation since there is absolutely no data on it while we do have a shitload of anecdotal information on other routes of administration.
https://en.wikipedia.org/wiki/Ischemic_colitis
Ischemic bowel is a potentially life threatening condition due to the risk of sepsis - You do not want shit to enter your blood stream. More on cocaine and amphetamine causing ischemic bowel.
0.1% of hospital administrations are due to ischemic colitis. The incidence is much higher, but many cases follow a mild course with spontaneous resolution. Once you have an ulcerous gangrenous rectum though there is comparably little hope for survival, even if you enter surgery within the hour which is recommended due to the highly acute nature of the condition, accompanied by treatment of the resulting sepsis.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2778113/
Ergo just do not administer stimulants rectally, especially not 3F-P which we have suspected to have significant local vasoconstrictive effects. This is the mechanism which I suspect to be responsible for the polyneuropathiae some people report (including myself), since nervous tissue is problematic in this scenario due to it's poor ability to autoregulate perfusion. Extensive necrosis can occur in nerve tissue within as little as 4 hours after administration of strong vasoconstrictors.
Due to the significant health hazards I would strongly discourage rectal administration of stimulants!
For those who do not take my advice seriously: If you experience rectal pain or bleeding after rectal administration of stimulants, stop right there. If it is followed by a fever seek medical care immediately, since mortality in this condition is extremely high and even with prompt medical care is rarely treated successfully.
@sekio
Sekio, you should know better than to blindly recommend methods of drug abuse that we have so little data on. You could have easily done some research to find out why transrectal administration of stimulants is to be discouraged. Especially before the background of you deleting my thread about passing amphetamine tests by consumption of salmiak two days ago.
I found that really low and we both know you did it because I called you respectless for telling people a traditional Northern European food is disgusting, not because salmiak consumption poses a significant health risk. Show me a single case of hospital administration due to acidosis caused by salmiak licorice ingestion!
Reducing the risk for potentially disastrous social consequences of drug abuse is an important aspect of harm reduction in my humble opinion and you were plain wrong to delete the thread, again in my humble opinion.
Now here you are suggesting very risky behaviour that you not only have no personal experience with, but did not bother to research. I suggest you edit your post in the spirit of harm reduction. I hope you keep enjoying your 'moderation' privileges the way you have!
May it never come to an end.