Gonal F works by delivering a lab-made version of follicle-stimulating hormone (FSH) directly into your body, which tells your ovaries to grow and mature egg-containing follicles — something your body isn't doing enough of on its own.

What Gonal F Does in Your Body

To understand how Gonal F works, it helps to know what FSH does naturally.

In a normal menstrual cycle, your pituitary gland (a small gland at the base of your brain) releases follicle-stimulating hormone (FSH) early in your cycle. FSH travels through your bloodstream to your ovaries, where it signals tiny fluid-filled sacs called follicles to start growing. Each follicle contains an immature egg. Usually, one follicle becomes dominant, matures fully, and releases an egg during ovulation.

Think of FSH like a growth signal for your eggs. Without enough of it — or if your ovaries don't respond well to it — follicles won't develop properly and ovulation may not happen.

Gonal F is a synthetic (recombinant) version of that same FSH. When you inject it, you're essentially giving your ovaries a stronger, more consistent growth signal than your body is producing on its own. Here's what happens step by step:

1. You inject Gonal F under the skin of your lower abdomen.
2. The follitropin alfa enters your bloodstream and travels to your ovaries.
3. It binds to FSH receptors on the surface of granulosa cells — the cells that surround and nourish your developing eggs.
4. This triggers follicle growth. The follicles start developing, and the granulosa cells begin producing estradiol (a form of estrogen), which thickens your uterine lining and signals that follicles are maturing.
5. Multiple follicles grow (especially in IVF protocols, where higher doses are used). Your doctor monitors them with ultrasound and blood tests.
6. When follicles reach the right size (usually 17-22mm), a "trigger shot" (typically hCG) is given to cause the final maturation and release of the eggs.

A helpful analogy: if your ovaries are a garden and eggs are seeds, then FSH is the water and sunlight. Gonal F is like turning on a sprinkler system when the rain isn't coming — giving your garden exactly what it needs to grow.

For Men

In men with hypogonadotropic hypogonadism, Gonal F works similarly but targets the testes. FSH receptors on Sertoli cells (the cells that support sperm development) respond to the injected follitropin alfa by stimulating spermatogenesis — the production of new sperm. This use requires pre-treatment with hCG to prepare the testes.

How Long Does Gonal F Take to Work?

Gonal F doesn't work like a pill you take once and feel effects within hours. It's a gradual process:

• Ovulation induction: You typically start seeing follicle development within 5-7 days of starting injections. The full stimulation period lasts about 7-14 days before your doctor determines you're ready for a trigger shot or ovulation.
• IVF stimulation: Follicle growth is usually visible on ultrasound by day 4-6 of stimulation. The full stimulation phase lasts about 8-12 days. Your doctor monitors every 1-3 days and adjusts your dose based on how your ovaries respond.
• Men (spermatogenesis): This is a much slower process. It can take 3-6 months or longer of consistent Gonal F and hCG injections before sperm appear in semen. Full effect on sperm count may take up to 18 months.

How Long Does Gonal F Last in Your Body?

After a single subcutaneous injection, Gonal F has a half-life of about 24-48 hours. This means it takes about 1-2 days for half of the medication to be cleared from your system. That's why it's typically dosed once daily — the effects build up steadily over the stimulation period.

After you stop taking Gonal F, the medication clears your system within a few days, but the follicles it stimulated continue developing for a short period. This is why monitoring continues even after the last injection, and why your trigger shot timing is so important.

What Makes Gonal F Different from Similar Medications?

Several other medications are used for ovarian stimulation in fertility treatment. Here's how Gonal F compares:

Gonal F vs. Follistim AQ (Follitropin Beta)

Both are recombinant FSH products that work the same way. The main differences are the delivery device (Gonal F uses the Redi-ject pen; Follistim uses a cartridge-and-pen system) and the manufacturer (EMD Serono vs. Organon). Most fertility doctors consider them interchangeable, and many clinics will switch between them based on availability and cost.

Gonal F vs. Menopur (Menotropins)

Menopur contains both FSH and LH activity, while Gonal F is pure FSH. Some IVF protocols use Gonal F alone, while others combine Gonal F with Menopur to provide both hormones. Menopur is derived from purified human urine, whereas Gonal F is produced through recombinant technology.

Gonal F vs. Clomid (Clomiphene) or Letrozole

Clomid and Letrozole are oral medications that work indirectly — they trick your brain into producing more FSH on its own. They're less potent and less predictable than Gonal F but are much cheaper (a few dollars per cycle vs. hundreds or thousands). They're typically the first-line treatment, with Gonal F reserved for patients who don't respond or who need IVF. For more, see our guide to Gonal F alternatives.

Final Thoughts

Gonal F works by giving your body a direct supply of follicle-stimulating hormone — the key signal your ovaries need to grow and mature eggs. It's a well-understood medication that has helped millions of people build their families through fertility treatment. While the injection process can feel intimidating at first, understanding what the medication is actually doing in your body can make the experience feel more manageable.

Want to learn more? Read about Gonal F side effects, drug interactions, or uses and dosage. If you need help finding Gonal F at a pharmacy, Medfinder can help you check availability.