What Are Suppositories Made Of? Cocoa Butter, Glycerin and PEG Bases Explained

Each row gives the base, how it releases the active, roughly where it softens, and which products on this site use it, per their labels.

The two families are melt and dissolve. Fat bases melt at body temperature and need cold storage; glycerin and PEG dissolve in the small amount of fluid present and are indifferent to a cool room but sensitive to humidity or drying. Everything else on this page follows from that split.

Cocoa butter is the fat pressed from cacao beans, and it was the suppository base for a century because it does one thing perfectly: it is solid at room temperature and liquid at body temperature, with a narrow melting range in the low to mid 90s Fahrenheit. On the hemorrhoidal shelf it is more than a carrier. The Preparation H Suppositories Drug Facts label lists cocoa butter as a protectant active alongside phenylephrine as a vasoconstrictor; Calmol 4 pairs cocoa butter with zinc oxide, also as labeled protectants. A protectant coats irritated tissue and shields it, which is exactly what a melting fat does where it sits.

Its weaknesses are the same property seen from the other side. It melts in a warm bathroom, a car or a summer mailbox, which is why owners keep hemorrhoidal suppositories refrigerated and why the label permits it. It leaks an oily residue after insertion, which is why labels time use around bedtime and bowel movements. And cocoa butter can recrystallize into a whitish surface bloom after melting and re-hardening, cosmetic and harmless. The shelf built on it is ranked in the best hemorrhoid suppositories.

Hard fat is the label name for hydrogenated vegetable oil blends engineered to behave like cocoa butter with more consistency: a controlled melting point a little above cocoa butter's, no bloom, no batch-to-batch variation. It is the base in most drug-bearing suppositories, where the job is to release a precise milligram amount: bisacodyl 10 mg in Dulcolax, acetaminophen 80, 120 or 325 mg in FeverAll, miconazole 200 mg in a Monistat 3-Day ovule. The label's inactive ingredients line typically reads hydrogenated vegetable oil, sometimes with a small amount of another wax or oil.

Because the active is dispersed through a fat that was poured hot and cooled in a mold, hard fat is the base where two cautions apply. If the suppository melts fully and sits, the active can settle toward one end, so a re-hardened drug-bearing suppository that shows layers is an uneven dose. And cutting across the middle can split the dose unevenly, which is why the one label that directs a half, the Dulcolax direction for children 6 to under 12, is cut lengthwise. Both are covered in suppository melted: what to do and can you cut a suppository.

A glycerin suppository has no separate active and base. The Fleet Glycerin Suppositories Drug Facts label lists glycerin 2 g as the active ingredient and sodium stearate and purified water as the inactive ingredients. Sodium stearate is a soap; a small amount of it turns liquid glycerin into a firm, translucent solid that holds a bullet shape and dissolves in the rectum's moisture rather than melting. That is why a glycerin suppository still works in a cool room, why several labels say to moisten it with water before inserting, and why it is the most forgiving suppository to store: it softens in humidity and shrinks when dry, but it does not turn to liquid the way a fat base does.

It is also why glycerin gets latitude on this site's melted and cutting pages that drug-bearing suppositories do not: a misshapen glycerin suppository still carries its dose, since the dose is the suppository. The mechanism follows from the chemistry: glycerin is hygroscopic and hyperosmotic, drawing water into the lower bowel, which is what the label describes when it states a bowel movement generally follows in 15 minutes to 1 hour. Liquid glycerin applicators are glycerin in solution with no stearate needed. The glycerin shelf is ranked in the best glycerin suppositories.

Polyethylene glycol, PEG, is a synthetic, water-soluble polymer available in grades from liquid to hard wax, and suppository makers blend grades to get a base that stays solid well above body temperature and then dissolves in body fluid rather than melting. Its advantages are the mirror image of fat: it does not melt in a hot mailbox, it leaks the least because it dissolves into the fluid present rather than pooling as oil, and it is not damaged by a warm room. It shows up in some vaginal moisturizer inserts and some rectal products; the label's inactive line will say polyethylene glycol or list PEG grades.

Its cautions are drying and irritation. A PEG suppository draws water from tissue as it dissolves, which is why some labels or pharmacists advise moistening it with water before insertion, and why a very old PEG suppository can be hard and slow to dissolve. It is not interchangeable with a fat base in a homemade mold, a point that matters on the DIY page, how to make suppositories at home, where the honest answer is that a base is a formulation, not a kitchen substitution.

Some vaginal suppositories are not molded at all. Boric acid products such as pH-D Feminine Health 600 mg are a measured powder in a two-piece gelatin or vegetable-cellulose capsule, the same form as an oral supplement, which is precisely the danger: it looks like something to swallow, and boric acid is poisonous if swallowed. The capsule dissolves in vaginal fluid and releases the powder. Every box carries the same warnings, and this page repeats them: for vaginal use only, never taken by mouth, keep away from children, do not use if pregnant or nursing, do not use on broken skin, stop and see a clinician if symptoms persist, and see a clinician for a diagnosis before self-treating. Boric acid is not FDA-approved to treat any condition; the labels describe it as for vaginal odor or pH balance support, and that is all we say about it.

Capsules want dry storage, not the refrigerator, because humidity makes the shell tacky and the powder clump. They are never opened: opening spills the dose and puts the powder on hands and surfaces. Some probiotic inserts use the same capsule form and may direct refrigeration to keep cultures viable; the label decides. The full safety note lives in the boric acid guide, and storage by base is in how to store suppositories.