@moliere about your comment on glycerin and stearic acid: did you actually try that? I know it works to use soap as a base for glycerin. But as far as I understand it, stearic acid still needs to react with e.g. potassium bicarbonate to become soap. Does stearic acid on its own work?
BTW I'm not questioning your knowledge, I'm just trying to clarify this. I would like to try it.
No, didn't seem worth it. I imagine that homemade glycerin suppositories are more potent and "kickier" than what you get now so maybe... though I haven't done it yet. Recipe came from an old edition of the USP. If you don't want to scavenge around for the PDF I did find extracts online, see https://www.henriettes-herb.com/eclectic/kings/glycerina_supp.html
Here's the official 1919 U.S.P. recipe:
SUPPOSITORIA GLYCERINI
Suppositories of Glycerin
Supp. Glycerin.
GLYCERIN, thirty grammes (30.0 Gm.)
Monohydrated Sodium Carbonate, ½ gramme (0.5 Gm.)
Stearic Acid, two grammes (2.0 Gm.)
WATER, five milliliters (5.0 mils)
To make ten rectal suppositories (10) Dissolve the monohydrated sodium carbonate in the water and add it to the glycerin contained in a suitable vessel placed in a water bath in such a way that the vessel is well down in the boiling water and its contents protected as much as possible from the steam of the bath. Add the stearic acid and heat the mixture for fifteen minutes or until the carbon dioxide ceases to be evolved, and the liquid is clear. Then pour the melted mass into suitable moulds, remove the suppositories when they are completely cold, and preserve them in tightly-stoppered glass vessels in a cool place.
If you want to try the Euro style gelatin ones start with glycerinated gelatin:
GELATINUM GLYCERINATUM / Glycerinated Gelatin / Gelat. Glycerin.
GELATIN, one hundred grammes (100 Gm.)
GLYCERIN, one hundred grammes (100 Gm.)
WATER, a sufficient quantity,
______
To make two hundred grammes (200 Gm)
Pour upon the gelatin sufficient water, which has been previously boiled and cooled, to cover it; allow it to stand one hour; pour off the water and allow the gelatin to drain for a few minutes; then transfer it to a dish, add the glycerin, and heat it on a water bath until the gelatin is dissolved. Strain the solution while hot, transfer to a tared dish* and continue the heat on the water bath until the product weighs two hundred grammes. When cold, out the mass into pieces, and preserve them in well-closed container
*meaning a dish that you know the weight/mass of so you can tell when the contents reduce to 200 gms.
To use as a laxative suppository add more glycerin and pour into a mold, start with 100 Gm. Additional glycerin, going up to 200 gms. Fully made this recipe will give you about 30-50 suppositories depending on size.