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Allylestrenol - Uses, Dosage, Side Effects, Drug Warnings, and Precautions

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Allylestrenol is a steroid with progestational activity and is used for maintaining pregnancy. This article reviews its uses, side effects, and indications.

Medically reviewed by

Dr. Sanap Sneha Umrao

Published At May 8, 2023
Reviewed AtApril 1, 2024


Studies have confirmed that in women experiencing threatened pregnancies, Allylestrenol was utilized as a treatment option. The results indicated that the drug is effective in maintaining pregnancy in a large group of patients who were not admitted to the hospital and is considered safe for both the mother and the child. However, it should be noted that Allylestrenol is ineffective in maintaining pregnancy in the presence of placental dysfunction. Infants born to mothers treated with Allylestrenol had slightly higher birth weights compared to the control group. Moreover, it was observed that at higher doses, the drug was able to effectively prevent premature labor, which suggests a selective impact on the myometrium.

How Does Allylestrenol Work?

Allylestrenol (AT) is an artificially synthesized progesterone that has been shown to be effective in treating abortion, preterm labor (TPTL), and intrauterine growth restriction. Research studies suggest that AT has a selective impact on the beta-adrenergic receptors on the myometrium, mediated by nerves, which helps reduce the myometrial activity. This effect leads to the rapid and efficient relaxation of hypertonic myometrium within 24 hours, ultimately preventing life-threatening emergencies for mothers such as pulmonary edema and myocardial ischemia. Due to its minimal side effects and high patient compliance, AT is considered a safe and effective drug for progesterone.


Allylestrenol is a synthetic progestin hormone that has several medical uses. Its uses include:

  • Preterm Labor: It is used to prevent premature labor and delivery in women who have a history of preterm labor.

  • Threatened Miscarriage: Allylestrenol is used to prevent miscarriage in women who have had previous miscarriages or are experiencing symptoms of a threatened miscarriage.

  • Menstrual Disorders: Allylestrenol is also used to treat menstrual disorders such as heavy or irregular periods.

  • Hormone Replacement Therapy: It can be used in hormone replacement therapy to provide hormonal support to women who have low levels of progesterone.

  • Endometriosis: Allylestrenol can be used to treat endometriosis, a condition where the tissue that normally lines the inside of the uterus grows outside the uterus.

  • Intrauterine Growth Restriction: Allylestrenol is used to improve fetal growth and development in women with intrauterine growth restriction, a condition where the fetus is not growing at the expected rate.

  • Benign Prostatic Hyperplasia: It is also used in men to treat benign prostatic hyperplasia.


  • Threatened Miscarriage: Five milligrams (mg) three times a day until symptoms subside, followed by a maintenance dose of five milligrams twice daily for two to three weeks.

  • Habitual Abortion: Five milligrams twice a day until the end of the 16th week of pregnancy.

  • Infertility: Five milligrams three times a day from the 5th to the 25th day of the menstrual cycle.


The drug Allylestrenol has several hazards associated with it, indicating its potential health risks:

  • Acute Toxicity on Oral Ingestion - The drug Allylestrenol is harmful if swallowed, with acute toxicity upon oral ingestion.

  • Acute Toxicity on Skin Exposure - The drug Allylestrenol is harmful if in contact with skin, with acute toxicity upon dermal exposure.

  • Acute Toxicity on Inhalation - The drug Allylestrenol is harmful if inhaled, with acute toxicity upon inhalation.

  • Carcinogenic - The drug Allylestrenolis suspected of causing cancer, with potential carcinogenicity.

For Patients:

Learn About the Maintenance of Pregnancy

Maintenance of pregnancy refers to the ability of a woman's body to sustain the growth and development of a fetus until full-term delivery (37 to 42 weeks). The maintenance of pregnancy requires a complex interplay of hormones and physiological changes to support the growth and development of the fetus while also ensuring the well-being of the mother. Hormones such as progesterone play a crucial role in maintaining pregnancy by relaxing the uterine muscles and preventing premature contractions. Other factors such as adequate nutrition, rest, and proper prenatal care are also essential for the maintenance of pregnancy. Any disruptions or complications during pregnancy can lead to preterm labor, miscarriage, or other adverse outcomes for both the mother and the baby.

Threatened premature labor (TPTL) refers to giving birth in the middle and late stages of pregnancy before normal delivery, which is defined as birth before 37 weeks. It is reported that approximately 65 percent of pregnant women with TPTL will give birth prematurely, while TPTL accounts for approximately 30 percent of hospitalizations related to pregnancy.

Spontaneous premature labor is responsible for approximately 30 percent of premature births, and only about ten to 15 percent of women with symptoms of premature labor will give birth within the next two to seven days. Developing more effective treatment methods for premature labor is a crucial issue that requires clinical attention.

Why and When Is Allylestrenol Required?

The leading cause of perinatal morbidity and mortality is threatened premature labor (TPTL). Gestational age at birth is negatively correlated with neonatal mortality, respiratory distress syndrome, intraventricular hemorrhage, and other diseases. Allylestrenol (AT) can effectively prolong the pregnancy time of TPTL patients by reducing the messenger nucleotide level of the oxytocin receptor. While progesterone has limited effects on acute uterine contraction, it may play a role in preventing premature delivery or serve as a sensitizer for other uterine contraction agents. It is crucial to find effective clinical treatments for TPTL to avoid threatening the life and health of newborns and to support their cognitive growth.

Learn More About Allylestrenol

Things to Tell Physicians Before They Prescribe Allylestrenol:

  1. Inform the healthcare provider about any ongoing medical conditions or medications, including over-the-counter drugs, vitamins, and herbal supplements.

  2. Some medical conditions that may be affected by Allylestrenol include kidney disease, liver disease, diabetes, hypertension, asthma, and heart disease. The physician will need to adjust the dosage or monitor the patient closely if they have any of these conditions.

  3. It is also important to tell the physician if the patient is pregnant, planning to become pregnant, or breastfeeding, as Allylestrenol may have an impact on fetal development and milk production.

  4. In addition, inform the physician if the patient has a history of stroke, blood clots, or cancer, as Allylestrenol may increase the risk of these conditions.

  5. Be sure to mention the presence of any allergies, especially to progestins or any other medications.

How Effective Is Allylestrenol in Maintaining Pregnancy?

  • Typically, embryos are not rejected by their mothers due to the immune tolerance at the mother-fetus interface and the balance of cytokines. However, when this immune tolerance is disrupted, habitual abortion can occur.

  • Pregnancy is a vulnerable period for both mothers and fetuses, as infections in the cervical vagina or uterus can lead to a pro-inflammatory environment that damages the immune privilege in the uterus.

  • About 30 percent of premature women experience microbial invasion or inflammation in the amniotic cavity, which disrupts fetal tolerance by increasing interleukin and tumor necrosis factor.

  • Progesterone, especially during bed rest, has a significant immunoregulatory effect that supports physiological immune tolerance. It affects interleukin production in vaginal and cervical epithelial cells, inhibits stimulation of interleukin production from bacterial activity in vaginal epithelial cells, and causes changes in inflammatory factor concentrations in cervical secretions.

  • The changes in IL-17, IL-10, and IL-6 levels of these factors are significantly reduced after treatment with Allylestrenol.

  • The use of Allylestrenol is effective in reducing the levels of inflammatory factors, preventing immune destruction, and maintaining body balance.

How to Take Allylestrenol?

Allylestrenol is a prescription medication and should be taken exactly as directed by the physician. The recommended dosage and duration of treatment may vary depending on the individual's medical condition.

Allylestrenol tablets are typically taken orally. The tablets are meant to swallow with a full glass of water, without crushing or chewing it. In case of a missed dose, the tablet must be taken as soon as it is remembered. Suddenly stopping the medication without consulting the physician can lead to unwanted side effects or the return of the symptoms.

How Effective Is Allylestrenol When Compared to Other Medications?

Allylestrenol (AT) is a medication that is commonly used as a synthetic progestin, which means it has similar effects to the hormone progesterone. It is often used to treat a variety of gynecological conditions, including threatened miscarriage, habitual abortion, and preterm labor.

Compared to other progestins, Allylestrenol is generally considered to have minimal side effects and good patient compliance. Some side effects may occur that include headache, nausea, and fatigue.

Things to Do After Starting Allylestrenol:

  • Follow the Physician’s Instructions: Take Allylestrenol exactly as directed by the physician.

  • Keep a Track of the Symptoms: Monitor any changes in the medical condition while taking Allylestrenol.

  • Attend All Scheduled Appointments: Keep all scheduled appointments with the physician to monitor the response to Allylestrenol and adjust the dosage if necessary.

  • Inform the Physician of Any Other Medications or Supplements: In case of starting any new medications or supplements, inform the physician to ensure there are no interactions with Allylestrenol.

  • Report Any Side Effects: In case of any side effects while taking Allylestrenol, notify the physician immediately. Some common side effects may include headache, nausea, and fatigue, but more serious side effects may also occur.

  • Store the Medication Properly: Keep Allylestrenol in a cool, dry place and out of reach of children.

  • Follow Healthy Habits: Maintain a healthy lifestyle by eating a balanced diet, getting regular exercise, and avoiding smoking and excessive alcohol consumption. This can help maximize the effectiveness of Allylestrenol and minimize potential side effects.

Look Out for the Side Effects:

Some common side effects of Allylestrenol include:

  • Nausea.

  • Headache.

  • Abdominal pain.

  • Fatigue.

  • Dizziness.

  • Edema (swelling).

  • Breast tenderness.

Serious side effects in rare cases may occur, such as:

  • Liver damage.

  • Allergic reactions.

  • Thrombosis (blood clot).

  • Jaundice.

  • Changes in mood or behavior.

For Doctors


Allylestrenol is primarily used in gynecology for the prevention of miscarriage and premature labor. It works by supporting the pregnancy and preventing the uterus from contracting prematurely.

In addition to its use in gynecology, Allylestrenol has also been investigated for its potential use in men for the treatment of benign prostatic hyperplasia (BPH). BPH is an enlargement of the prostate gland that leads to urinary symptoms such as frequent urination and difficulty urinating. Allylestrenol has been found to help reduce the size of the prostate gland and improve urinary symptoms in some men with BPH.


  • Mechanism of Action: Allylestrenol has a structure and function similar to progesterone, and shares the pharmacological actions of the progestins. The receptors for progesterone and estrogen are present in target cells including the female reproductive tract, hypothalamus, pituitary, and mammary gland. Upon binding to the receptor, progestins like progesterone reduce the frequency of gonadotropin-releasing hormone (GnRH) release from the hypothalamus and suppress the pre-ovulatory LH (luteinizing hormone) surge. Progesterone plays an essential role in the development of decidual tissue and increases the endometrial receptivity for embryo implantation. After implantation, progesterone helps maintain the pregnancy.

  • Pharmacodynamics: Allylestrenol is a progestogen that is chemically similar to progesterone. It is commonly used to treat threatened and recurrent miscarriages, as well as to prevent premature labor. However, its use is now limited to cases of proven progesterone deficiency, and it is not recommended for routine use in these conditions. For women with progesterone deficiency experiencing threatened miscarriage, a suggested dosage is five milligrams taken orally three times daily for a period of five to seven days.

  • Absorption, Metabolism, and Elimination: The urine and bile excrete the glucuronide and sulfate conjugates of pregnanediol and pregnanolone. Progesterone metabolites are excreted in bile and may be passed through feces. The kidneys are the primary excretory route for progesterone metabolites.

Warnings and Precautions:

  • Before using Allylestrenol, it is important to receive special instructions and thoroughly understand all safety precautions.

  • Take measures to prevent mixing with flammable materials and use appropriate personal protective equipment as needed.

  • If ventilation is insufficient for the patient then wearing respiratory protection is mandatory.

  • Seek medical attention in case of any adverse effects.

  • If breathing difficulty occurs, move to an area with fresh air and rest in a comfortable position.

  • In the event of ingestion of Allylestrenol, immediately contact a poison control center or doctor.

  • If Allylestrenol comes in contact with the skin, wash gently.

  • If Allylestrenol is inhaled, call a poison control center or doctor.

Dosage and Administration:

  • To Control Heavy and Unusual Bleeding- For adults and teenagers, the recommended dosage is five to ten milligrams (mg) per day for five to ten days or ten milligrams mg. For adults and teenagers, the recommended dosage is five to ten milligrams (mg) per day for five to ten days or ten milligrams as directed.

  • Endometrial Hyperplasia- For adults, the recommended dosage is five to ten milligrams per day for ten to fourteen or more days each month as directed by a doctor.

  • Endometriosis- For adults and teenagers, the recommended dosage is 2.5 to 10 mg per day as directed by a doctor. The dosage may be for five to ten days only or for a longer duration depending on the doctor's instructions.

Considerations for Administration:

  • Allylestrenol is available in tablet form and is typically taken orally.

  • The recommended dosage and duration of treatment will vary depending on the specific condition being treated.

  • Allylestrenol is generally well-tolerated, but like all medications, it can cause side effects.

  • Allylestrenol is not recommended for use during the first trimester of pregnancy, as there is limited data on its safety during this time. It may be used during the second and third trimesters if the potential benefits outweigh the risks.

  • In case of a missed dose if it is close to the time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not double up on doses.


  • Hypersensitivity: Allylestrenol should not be used in individuals who have a known hypersensitivity or allergy to the drug or any of its ingredients.

  • Thromboembolic Disorders: Allylestrenol should not be used in individuals with a history of thromboembolic disorders such as deep vein thrombosis, pulmonary embolism, or stroke.

  • Liver Disease: Allylestrenol is metabolized in the liver, and thus should be used with caution in individuals with liver disease.

  • Undiagnosed Vaginal Bleeding: Allylestrenol should not be used in individuals with undiagnosed vaginal bleeding, as this can be a symptom of an underlying condition that may require alternative treatment.

  • Breast Cancer: Allylestrenol should not be used in individuals with a history of breast cancer or other estrogen-sensitive malignancies.

  • Pregnancy and Lactation: Allylestrenol should not be used during pregnancy or lactation unless specifically recommended by a healthcare provider.

Drug Interactions:

Allylestrenol may interact with other ongoing medications, vitamins, or herbal supplements. It is important to inform the doctor about all the ongoing medications, including prescription and over-the-counter drugs, as well as any herbal supplements and vitamins. Some drugs that may interact with Allylestrenol include:

  • Anticoagulants (blood thinners) like Warfarin.

  • Rifampicin and other drugs induce hepatic microsomal enzymes, which can reduce Allylestrenol's effectiveness.

  • Anticonvulsants like Phenobarbital, Phenytoin, Carbamazepine, and Primidone.

  • Anti-infectives like Erythromycin and Tetracyclines.

Other Specifications

  • Allylestrenol During Pregnancy: Progesterone is a hormone produced naturally by the body during pregnancy and has not been associated with any adverse effects. It is sometimes used to treat infertility in women and to support egg donors or infertility procedures.

However, the effects of other progestins on pregnant women have not been studied extensively. It is advisable to use birth control while receiving high doses of progestin since these doses have been linked to birth defects in the sex organs of male fetuses. Low doses of progestins, such as those used for contraception, have not been associated with any significant problems if used accidentally during pregnancy.

  • Breastfeeding and Allylestrenol: While progestins can pass through breast milk, there is no evidence to suggest that they cause any harm to nursing infants. However, the use of progestins may alter the quantity or quality of breast milk produced by the mother. Depending on the specific case, it may be necessary to discontinue breastfeeding or take alternative medications during treatment.

  • Allylestrenol in Geriatric Patients: Studies have indicated that progestin does not cause distinct adverse effects or issues in older individuals compared to younger adults.

Source Article IclonSourcesSource Article Arrow
Dr. Sanap Sneha Umrao
Dr. Sanap Sneha Umrao

Obstetrics and Gynecology


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