Is a Susten Injection a Steroid? Understanding Progesterone vs. Other Steroids

October 7, 2025 •

4 min read

While commonly misunderstood, a Susten injection, which contains the hormone progesterone, is indeed a type of steroid. However, its function and effects differ significantly from the anabolic or corticosteroid steroids people often associate with the term 'steroid,' and it is primarily used for female reproductive health.

Quick Summary

Susten injections contain progesterone, a natural steroid hormone used for female infertility and menstrual disorders. This steroid supports pregnancy and regulates the menstrual cycle, functioning differently from anabolic or corticosteroid medications.

Key Points

Yes, Susten is a Steroid Hormone: Susten contains progesterone, which is a female sex steroid hormone.
Not an Anabolic or Corticosteroid: Progesterone has a reproductive function and is distinctly different from anabolic steroids (used for muscle growth) and corticosteroids (used for inflammation).
Used for Reproductive Health: Susten injections are prescribed for issues like female infertility, abnormal uterine bleeding, and supporting early pregnancy.
Mechanism of Action: It works by increasing progesterone levels to thicken the uterine lining and help maintain a pregnancy.
Side Effect Profile Differs: Unlike corticosteroids, side effects for progesterone injections typically include breast tenderness, mood swings, and injection site reactions, not the more serious long-term effects of chronic corticosteroid use.

What is a Susten Injection?

A Susten injection is a brand name for a medication containing progesterone, a naturally occurring female sex hormone. It is primarily prescribed to women to address issues related to hormonal imbalance and support fertility. The injection helps increase the body's progesterone levels, which plays a critical role in regulating the menstrual cycle, supporting the uterine lining, and maintaining early pregnancy.

The Role of Progesterone

Progesterone is one of the primary female sex hormones, produced in the ovaries, adrenal glands, and placenta. Its purpose is to prepare the body for conception and pregnancy. Following ovulation, the corpus luteum in the ovary produces progesterone, which thickens the uterine wall to prepare it for the implantation of a fertilized egg. If pregnancy does not occur, progesterone levels drop, triggering menstruation. During a successful pregnancy, progesterone production continues to prevent uterine contractions and maintain the pregnancy.

Is Progesterone a Steroid?

Yes, progesterone is chemically classified as a steroid hormone because its molecular structure is derived from cholesterol. The term "steroid" refers to a specific molecular class characterized by a four-ringed carbon structure. This classification includes many different hormones, including sex hormones (like estrogen and testosterone) and corticosteroids.

Distinguishing Steroid Types: Progesterone vs. Corticosteroids

It's important to understand that not all steroids have the same function. The medical world differentiates between different classes of steroids based on their actions in the body. When many people hear the word "steroid," they think of either anabolic steroids, which can be misused for muscle growth, or corticosteroids, which are used to treat inflammation. Progesterone falls into a distinct category with a very different purpose.


Feature	Progesterone (in Susten)	Corticosteroids (e.g., Prednisone)
Primary Function	Regulates female reproductive cycle, supports early pregnancy.	Acts as a potent anti-inflammatory and immunosuppressant.
Chemical Type	A female sex steroid hormone.	A class of adrenal hormones.
Therapeutic Use	Female infertility, menstrual disorders, hormone replacement therapy.	Arthritis, asthma, inflammatory bowel disease, allergies.
Side Effects	Breast tenderness, mood swings, weight changes, headache, injection site pain.	Weight gain, high blood pressure, diabetes, osteoporosis, cataracts with long-term use.

Therapeutic Uses of Susten Injection

Susten injections are used for several specific medical purposes, all related to a deficiency of or need for progesterone.

Support for Early Pregnancy: It is used to maintain pregnancy, especially in cases where a patient has a history of recurrent miscarriage linked to luteal phase defects.
Luteal Phase Support in IVF: During in vitro fertilization (IVF), Susten is administered to support the luteal phase and enhance the chances of a successful implantation.
Menstrual Cycle Regulation: It can be used to restart regular menstrual cycles in women with secondary amenorrhea (missed periods).
Treatment of Abnormal Bleeding: Susten can help manage dysfunctional uterine bleeding by controlling hormone levels.

How Susten Works

The active ingredient, progesterone, works by binding to progesterone receptors in the body. In the context of fertility and pregnancy, its main actions are centered on the uterus:

Endometrial Maturation: It causes the lining of the uterus (the endometrium) to mature and thicken, making it more receptive to a fertilized egg.
Uterine Relaxation: Progesterone helps relax the smooth muscles of the uterus, which is crucial for preventing preterm labor and maintaining pregnancy.
Hormonal Balance: It helps correct hormonal imbalances that may lead to irregular bleeding or other menstrual disorders.

Potential Side Effects

Like any medication, Susten injections can cause side effects. These are typically different from the side effects associated with corticosteroids and include:

Common Side Effects: Injection site reactions (pain, swelling), headaches, dizziness, fatigue, breast tenderness or pain, bloating, and mood changes.
Less Common/Serious Side Effects: While rare, more serious issues can include severe depression, allergic reactions, or blood clots. It is crucial to inform your doctor of any unusual or severe symptoms.

Conclusion

In conclusion, a Susten injection is a steroid, but it contains the female reproductive hormone progesterone, not a corticosteroid or anabolic steroid. This distinction is critical for understanding its therapeutic purpose and side effect profile. Used primarily for infertility treatment and pregnancy support, Susten helps correct progesterone deficiencies and maintain a healthy uterine environment. It is vital to use this medication only under the direct supervision of a healthcare provider to ensure proper dosage and management of any potential side effects. The perception that all steroids carry the same risks and functions is a misconception that can lead to confusion and fear regarding necessary medical treatments.

For more detailed information on progesterone, consult the National Library of Medicine's (NIH) comprehensive article on its physiology.

Frequently Asked Questions

A Susten injection contains the female sex hormone progesterone and is used for fertility and menstrual issues. A cortisone shot contains a corticosteroid, a different type of steroid used for its potent anti-inflammatory properties, such as in cases of arthritis.

Susten is used to treat female infertility, regulate irregular menstrual cycles, and support early pregnancy. It is prescribed for conditions like secondary amenorrhea and dysfunctional uterine bleeding.

No, Susten is not an anabolic steroid. Anabolic steroids are a different class of hormones that promote muscle growth. Susten contains progesterone, a female sex steroid hormone that regulates reproductive functions.

A progesterone injection increases the body's progesterone levels. This helps to prepare the uterine lining for a fertilized egg's implantation, prevents uterine contractions, and is crucial for maintaining early pregnancy.

Susten is often prescribed to help maintain early pregnancy, especially in cases of threatened abortion or recurrent miscarriages due to luteal phase defects. However, it should only be used under the strict guidance and supervision of a doctor, who will weigh the benefits and risks.

Common side effects include injection site reactions (pain, swelling), headaches, dizziness, fatigue, breast tenderness, bloating, and mood changes.

Susten is typically administered as an intramuscular injection, meaning it is injected into a muscle mass. This is usually done by a healthcare provider, or a patient can be taught to self-administer at home.

While weight changes are a potential side effect of progesterone, any effect is generally not as significant as the weight gain associated with long-term use of corticosteroids. Other common progesterone side effects like bloating and fluid retention may cause slight fluctuations.