Follistim and Gonal-F are not the same medication, but they are extremely close. Both are lab-made versions of follicle-stimulating hormone (FSH), the hormone your body naturally produces to grow egg follicles in the ovaries. They work the same way, produce nearly identical pregnancy outcomes, and are used interchangeably in fertility treatment. The key difference is subtle: Follistim contains follitropin beta, while Gonal-F contains follitropin alfa. These are two slightly different formulations of the same hormone, made by two different pharmaceutical companies.
What Makes Them Different
Both drugs are manufactured using the same basic technology. Chinese hamster ovary (CHO) cells are genetically engineered to produce human FSH, which is then purified into an injectable medication. The difference comes down to how sugar molecules attach to the protein during manufacturing, a process called glycosylation. Gonal-F (follitropin alfa) is slightly more acidic than Follistim (follitropin beta) because of small variations in these sugar chains, particularly in the number of sialic acid residues on the surface of the molecule.
The two drugs also differ in potency per milligram of protein. Follitropin alfa has a specific activity of about 13,636 IU per milligram, while follitropin beta comes in at around 10,000 IU per milligram. In practice, this doesn’t matter to you as a patient because your doctor prescribes a specific IU dose regardless of the brand, and the medication is already measured out in those units.
Pregnancy Rates Are Virtually Identical
The question most people really want answered is whether one works better than the other. A large retrospective study comparing the two in IVF cycles found no meaningful difference. Cumulative live birth rates were 52.8% with Gonal-F versus 55.7% with Follistim, a gap that was not statistically significant. After adjusting for patient characteristics, the type of FSH used had essentially zero association with live birth outcomes (the odds ratio was 1.01, meaning perfectly even).
Fresh embryo transfer results were also nearly identical: live birth rates of 38.1% per transfer with Gonal-F compared to 39.1% with Follistim. For frozen embryo transfers, the numbers were 55.2% and 57.9%, respectively. None of these differences reached statistical significance. The number of eggs retrieved was also comparable between the two drugs, though one finding did stand out: patients on Gonal-F tended to use a slightly lower total dose than those on Follistim to achieve similar results.
Who Makes Each Drug
Gonal-F is manufactured by EMD Serono, a division of the global pharmaceutical company Merck KGaA (based in Germany, not to be confused with the American Merck). Follistim is made by Organon, a company that spun off from the Dutch pharmaceutical giant MSD/Merck & Co. The two drugs have been competing in the fertility market for decades, and your clinic may stock one or both.
How They Come Packaged
Both medications are available as prefilled injection devices designed for subcutaneous (under the skin) self-injection. Follistim AQ comes in single-patient-use cartridges of 300 IU, 600 IU, and 900 IU, which load into a reusable pen injector. Gonal-F RFF is available in prefilled pens across a range of doses. Both systems use small needles and are designed so patients can inject at home without help from a nurse.
If your doctor switches you from one to the other mid-cycle or between cycles, the pen device will be different. The cartridges are not interchangeable between the two pen systems, so you’ll need to learn the new device. Your clinic or pharmacist will walk you through it.
Side Effects
Because both drugs deliver the same hormone, their side effect profiles overlap almost completely. The most common issues include bloating, mild pelvic discomfort, headache, and injection site reactions like redness, pain, or bruising. Ovarian hyperstimulation syndrome (OHSS), a condition where the ovaries overreact and swell, occurred in about 6.8% of women in Gonal-F clinical trials for ovulation induction. Follistim carries the same OHSS risk since it stimulates follicle growth through the same mechanism.
Your risk of OHSS depends far more on your individual response, your age, your ovarian reserve, and how aggressively your protocol is dosed than on which brand of FSH you use.
Storage
Both medications should be stored in the refrigerator at 2°C to 8°C (about 36°F to 46°F) before first use. Gonal-F can also be kept at room temperature (up to 25°C or 77°F) for a limited period. Once a cartridge or pen is in use, check the specific product labeling for how long it stays stable outside the fridge. If you’re traveling during a treatment cycle, a small insulated cooler bag with an ice pack is usually sufficient to keep either medication at the right temperature.
Why Your Clinic Might Prefer One Over the Other
Doctors rarely have a strong clinical preference between the two because the outcomes data is so similar. The choice often comes down to which drug your insurance covers, which one your pharmacy can get at a better price, or which pen system your clinic is most comfortable teaching patients to use. If you’re paying out of pocket, it’s worth checking prices at specialty pharmacies for both brands, as costs can vary significantly. Some patients also find one pen device easier to use than the other, which is a perfectly valid reason to prefer it.
If your doctor does switch you between brands, the transition is straightforward. The IU dosing carries over directly, and no additional monitoring is needed simply because of the brand change.