Progesterone exerts its actions by binding with an intracellular progesterone receptor. It is important to note that a number of physiological effects of progesterone are amplified in the presence of estrogen. (This is also the reason why we sometimes give estrogen in addition to progesterone to patients in the second half of the cycle (luteal phase)).
What are the actions of progesterone?
Sperm
- Progesterone may have an effect on sperm motility.
- Since eggs release progesterone, sperm may use progesterone as a homing signal to swim toward eggs.
Pregnancy
- Progesterone converts the uterine lining (endometrium) to its secretory stage to prepare it for implantation.
- Progesterone may decrease the maternal immune response to allow for the acceptance of the pregnancy
- It decreases uterine contractility. It may therefore prevent miscarriage or preterm labor.
- It inhibits lactation during pregnancy. Fall in progesterone levels following delivery is one of the triggers for milk production.
- A drop in progesterone levels may be associated with the onset of labor.
Other actions
- It increases core temperature during ovulation. This is how basal body temperature (BBT) charts are used to document ovulation. One should note that the temperature rise sometimes occurs a day or two AFTER ovulation. BBT charts are therefore NOT useful to time intercourse to optimize chances of conception. In fact, they may result in the couple actually missing the most fertile period.
- It prevents endometrial (uterine lining) cancer by regulating the effects of estrogen. This is why patients who do not get periods (polycystic ovarian disease, PCO) are advised to take progesterone pills to induce a menses at least 3 – 4 times a year.
Side effects of progesterone
The side effects of progesterone can vary based on how it is administered. Oral progesterone can make you drowsy. The intramuscular injections can cause local allergic reactions – these are often to the oil that is used (peanut, sesame, olive, ethyl oleate) and switching to a different preparation may solve the problem. With the vaginal gel there can be a white vaginal discharge and irritation. The vaginal tablets also can cause local irritation.
Some of the common side effects include headache, breast tenderness or pain, upset stomach, vomiting, diarrhea, constipation, tiredness, muscle, joint or bone pain, mood swings, irritability, excessive worrying, runny nose, sneezing, cough, problems urinating.
Some side effects can be serious. These are uncommon, but if you experience any of them, call your doctor immediately. These include breast lumps, migraine headaches, severe dizziness or faintness, slow or difficult speech, weakness or numbness of an arm or leg, lack of co-ordination or loss of balance, shortness of breath, fast heartbeat, sharp chest pain, coughing up blood, leg swelling or pain, loss of vision or blurred vision, bulging eyes, double vision, unexpected vaginal bleeding, shaking hands that you cannot control, seizures, stomach pain or swelling, depression, hives, skin rash, itching, difficulty breathing or swallowing, swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles or lower legs, hoarseness. Problems with abnormal blood clotting may cause serious problems affecting blood supply to the brain, heart, lungs or eyes.
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