What You Should Know About Pregnyl Side Effects

Pregnyl (chorionic gonadotropin, or hCG) is an injectable medication used in fertility treatment, cryptorchidism, and hypogonadotropic hypogonadism. Like any medication, it comes with side effects — some mild and manageable, others serious enough to need immediate medical attention.

This guide covers what to expect when taking Pregnyl, which side effects are normal, and the warning signs that mean you should call your doctor right away.

What Is Pregnyl?

Pregnyl is a brand-name form of human chorionic gonadotropin (hCG), a hormone naturally produced during pregnancy. It's manufactured by Organon and given as an intramuscular (IM) injection. In women, Pregnyl triggers ovulation. In men, it stimulates testosterone production. For a deeper look at what this medication does and how it's used, see our guide on what Pregnyl is and how it works.

Common Side Effects

These side effects are relatively normal and usually don't require medical intervention unless they become severe:

• Injection site pain or swelling — The most common complaint. Pregnyl is given as an IM injection, and some soreness, redness, or bruising at the injection site is expected.
• Headache — Mild to moderate headaches are reported frequently, especially in the first few days after injection.
• Fatigue or restlessness — You may feel unusually tired or, conversely, restless and unable to sleep well.
• Mood changes and irritability — hCG affects hormone levels, which can cause mood swings, anxiety, or irritability.
• Bloating or mild pelvic discomfort — Especially common in women using Pregnyl for ovulation induction. Some degree of ovarian enlargement is expected.
• Water retention and edema — Mild swelling in the hands, feet, or ankles due to fluid retention.

Most of these side effects are temporary and resolve within a few days of the injection. If any become severe or don't improve, contact your doctor.

Serious Side Effects

The following side effects are less common but require prompt medical attention:

Ovarian Hyperstimulation Syndrome (OHSS)

OHSS is the most significant risk associated with Pregnyl in women. It occurs when the ovaries overrespond to hormonal stimulation. Mild OHSS causes bloating and discomfort, but severe OHSS can be life-threatening.

Call your doctor immediately if you experience:

• Severe pelvic or abdominal pain
• Rapid weight gain (more than 5 pounds in a day)
• Severe nausea, vomiting, or diarrhea
• Difficulty breathing or shortness of breath
• Decreased urination
• Swelling of the abdomen that feels tight or distended

OHSS typically develops within 5-10 days after the hCG injection. Your doctor should be monitoring you closely during this window.

Blood Clots (Thromboembolism)

Pregnyl can increase the risk of blood clots, particularly in women undergoing fertility treatment. Symptoms to watch for include:

• Sudden leg pain or swelling (especially one-sided)
• Chest pain or difficulty breathing
• Sudden severe headache or vision changes

Seek emergency medical care if you experience any of these symptoms.

Multiple Pregnancies

When used for ovulation induction, Pregnyl increases the chance of multiple pregnancies (twins, triplets, or more). While not a side effect in the traditional sense, this is a significant risk your doctor should discuss with you before treatment.

Ovarian Torsion

Enlarged ovaries from stimulation can twist on themselves, cutting off blood supply. This causes sudden, severe pelvic pain and is a medical emergency requiring immediate treatment.

Allergic Reactions

Though rare, anaphylactic reactions to Pregnyl have been reported. Seek emergency care if you experience:

• Difficulty breathing or swelling of the throat
• Hives or widespread rash
• Rapid heartbeat or dizziness

Precocious Puberty (Pediatric Patients)

In boys treated for cryptorchidism, hCG can occasionally trigger early puberty. Signs include rapid growth, development of body hair, or deepening of the voice. Report these changes to your child's doctor.

Side Effects in Specific Populations

Women Using Pregnyl for Fertility

Women are at the highest risk for OHSS, especially those with polycystic ovary syndrome (PCOS) or those who produced many follicles during stimulation. Your fertility clinic should monitor you with blood tests and ultrasounds throughout your cycle.

Men Using Pregnyl for Hypogonadism

Men may experience acne, breast tenderness or gynecomastia, and mood changes. These are related to increased testosterone production. In rare cases, men may develop fluid retention that worsens heart or kidney conditions.

Patients with Heart or Kidney Disease

Pregnyl can cause fluid retention, which may worsen existing cardiac or renal conditions. Your doctor should monitor you more closely if you have a history of these issues.

How to Manage Common Side Effects

• Injection site pain: Apply ice to the area for 10-15 minutes after injection. Rotate injection sites. Let the medication reach room temperature before injecting.
• Headache: Over-the-counter acetaminophen (Tylenol) is generally safe. Check with your doctor before taking ibuprofen or aspirin, especially if you're in a fertility cycle.
• Bloating: Stay hydrated, eat smaller meals, avoid high-sodium foods, and rest when needed.
• Mood changes: These are usually temporary. Let your support system know what to expect. If mood changes are severe, talk to your doctor.
• Fatigue: Get extra rest and avoid overexertion, especially during the days immediately following injection.

For more information about what Pregnyl is and how it works in your body, read our mechanism of action guide. And if you're having trouble finding Pregnyl at your pharmacy, check our guide on how to find Pregnyl in stock near you.

Final Thoughts

Most people tolerate Pregnyl well, and common side effects like injection site pain, headache, and bloating are manageable. The serious risk to be aware of — especially for women — is OHSS. Make sure your doctor has a monitoring plan in place, and don't hesitate to call if something feels wrong.

If you're concerned about the cost of Pregnyl alongside managing your treatment, our guide on saving money on Pregnyl has tips on coupons, discounts, and patient assistance programs.