progestin
Meaning of progestin: A manufactured hormone built to act like progesterone, and the second ingredient in almost every contraceptive pill.
Definition of progestin
A progestin is a manufactured hormone that acts on the same receptors as progesterone, the hormone the ovary produces after releasing an egg. Progestins appear in contraceptives, in hormone therapy after menopause, and in treatment of heavy or irregular bleeding. They are not identical to progesterone; each has a different molecular shape and a slightly different pattern of effects.
How does a progestin differ from progesterone?
| Progesterone | Progestin | |
|---|---|---|
| Source | Made by the ovary and the placenta | Made in a laboratory |
| Structure | One fixed molecule | Many different molecules |
| Taken by mouth | Broken down rapidly by the liver | Designed to survive that passage |
| Other receptors | Little activity elsewhere | Varies; some touch androgen receptors |
The practical problem the chemistry solved was survival. Swallowed progesterone is largely destroyed before it reaches the circulation, so altering the molecule was necessary to make an oral hormone work at a sensible dose.
What are they used for?
In contraception a progestin suppresses the signal that triggers release of an egg, thickens the mucus at the cervix so sperm cannot pass, and thins the lining of the womb. In hormone therapy after menopause it serves a protective purpose: estrogen alone drives the womb lining to thicken and raises the risk of cancer there, and adding a progestin counters that, which is why it is omitted for anyone whose womb has been removed. It is also used for heavy or irregular bleeding, for endometriosis, and released slowly from an intrauterine device or an implant.
Why are there so many?
Each was built from a different parent molecule, and the parentage shows in the effects. Some derive from testosterone and retain a trace of androgen activity, which can affect skin and lipid levels. Others derive from progesterone itself and behave more closely like it. One is built from spironolactone and blocks salt retention. The differences influence which is chosen, and how strongly each binds the progesterone receptor as against other hormone receptors is what separates them.
Also known as
Used in a sentence
The regimen combined an estrogen with a progestin to protect the lining of the womb.
Good to know
A progestin is not another name for progesterone; the molecules differ, and effects observed with one progestin do not automatically apply to another.
Word origin
Where “progestin” comes from
Built from the Latin pro, meaning for or on behalf of, and gestare, meaning to carry, a reference to the hormone's role in pregnancy.