RECTAL ABSORPTION OF CANNABINOIDS.
6/14/2016: UPDATED INFORMATION AND MULTIPLE BLOGS I HAVE SINCE WRITTEN SHOW THAT WHOLE PLANT CANNABIS IS NOT RECTALLY ABSORBED. THC CAN BE RECTALLY ABSORBED BUT ONLY IF BONDED TO A SEPARATE MOLECULE, SUCH AS HEMI-SUCCINATE.
MANY PATIENTS USE HIGH DOSES OF THC BY THE RECTAL ROUTE TO AVOID PSYCHOACTIVITY. THE REASON THERE IS NO PSYCHOACTIVITY IS BECAUSE IT IS NOT ABSORBED.
There has been talk recently in some circles about the potential usefulness of rectal cannabis. For the first portion of this blog, I will deal with the substantial anecdotal information I am aware of and I will include a reference that truly settles the issue. In my experience with patients, there are a number of patients that use hash rectally. They clearly get VERY stoned, so it is being absorbed. I have many patients with Inflammatory Bowel Disease. If the disease is in the lower bowel, rectal administration often works better than oral absorption. There are a number of reasons why this might be the case for many patients as the cannabinoids are absorbed from two areas of the rectum.
It makes no sense at all to me that the overall cannabinoid effect is less than sublingual when placed in ANY area of the rectum. However, if portal circulation is what is desired, a soft tip syringe placed in 1.5 inches will be drained by the Superior Rectal Vein and mostly go through the liver.
The potential REASONS for using rectal absorption means are:
1. No other method practical.
2. The physician wants to help the cannabinoid medicine travel through the local rectal and pelvic veins and lymphatics. When a patient has a rectal or pelvic disease, it makes sense that this might be more effective….i.e. follow the Cancer. We have NO proof of this, but we are often making decisions with less than adequate information…..and not just in the field of Cannabis Medicine
3. Inflammatory Bowel Disease when oral is not working well
4. Some seizure kids during emergency rectal CBD administration. BTW, this seems to work clinically.
The rectum has two venous drainage sources. As you can see in the above diagram of the rectum, there are three veins that drain the rectum. They are the Inferior Rectal Vein, The Middle Rectal Vein and the Superior Rectal vein.
The inferior and middle rectal veins drain primarily into the Inferior Vena Cava and are absorbed into the blood stream avoiding the first pass effect through the liver.
The Superior Rectal Vein drains into the Portal system, goes through the liver and is first pass metabolized.
So, it depends WHERE in the rectum the suppository or “syringe” is placed. The “suppository” image represents the 3 cm of the Rectum. So, if a typical suppository is inserted fully, it will be absorbed by all the veins and there will always be a portion, probably significant, that goes through the Portal Vein System into the liver.
Oral absorption is a bit more erratic in large part due to stomach acid interfering with absorption, but still very effective especially if delivered with fat and little other food. In my experience with oral CBD capsules, it is extremely important to take it on an empty stomach.
I find that many patients with bowel disease do just fine with oral absorption, but it is not surprising that some with large bowel and or rectal/sigmoid disease, that regional absorption with regional venous and lymphatic drainage is very helpful.
So, now for the data. There are a number of studies showing both oral and rectal absorption of similar doses of cannabinoids. It seems pretty clear that the bioavailability through rectal absorption is about twice that of oral absorption. There are many variables and we have much to learn, but rectal delivery of cannabis is not new and it will become more common as better and more reliable preparations are made available.