Cat insulin requires a veterinary prescription in the United States and can be purchased from your vet’s office, retail pharmacies, online pet pharmacies, or big-box stores with pharmacy counters. Where you buy it can make a significant difference in price, with retail pharmacies often charging 30% to 50% less than veterinary clinics for the same product.
You Need a Prescription First
All insulin used in cats is a prescription drug. The FDA requires that it be dispensed only by or on the lawful order of a licensed veterinarian. That means before you shop anywhere, you need your vet to diagnose your cat, select the right insulin type, and write a prescription. Most vets will provide a written prescription if you ask, even if they also sell insulin in-house. Some states require them to do so by law.
Once you have that prescription, you’re free to fill it wherever you find the best price and convenience.
Veterinary Clinics
The simplest option is buying directly from the vet who prescribed it. You walk out of the appointment with insulin in hand, and the staff can show you how to use the syringes and store the vial. The tradeoff is cost. Vet clinics typically mark up insulin to cover overhead, and prices vary widely even between clinics in the same city. A CBC News investigation in Vancouver found the same 10 mL vial of Lantus (glargine) priced anywhere from $125 to $175 at different veterinary offices, while retail pharmacies nearby sold it for $65 to $90.
Retail and Big-Box Pharmacies
Standard human pharmacies like CVS, Walgreens, Costco, Walmart, and grocery store pharmacies can fill prescriptions for cat insulin. This is especially relevant if your vet prescribes Lantus (glargine), which is a human insulin product used off-label in cats. Since these pharmacies already stock it for human patients, they can sell it at their standard price, which is often considerably lower than what a vet charges.
Costco and large discount pharmacies tend to offer the lowest prices. You don’t need a Costco membership to use their pharmacy in most states. Simply bring your vet’s prescription to the pharmacy counter and let them know it’s for your cat. Pharmacists fill veterinary prescriptions routinely.
For the FDA-approved veterinary insulins, ProZinc and Vetsulin, availability at human pharmacies is less consistent. These are manufactured specifically for animal use, so not every retail pharmacy stocks them. Call ahead before making the trip.
Online Pet Pharmacies
Online retailers like Chewy Pharmacy, 1-800-PetMeds, and PetCareRx sell both ProZinc and Vetsulin. They’ll contact your vet to verify the prescription, or your vet can send it directly. Shipping usually takes a few days, so this isn’t ideal for your first vial when you need to start treatment right away, but it works well for refills. Prices are generally competitive with retail pharmacies and sometimes lower.
When ordering online, make sure the pharmacy is accredited by the National Association of Boards of Pharmacy (NABP) or carries the Vet-VIPPS seal. This confirms they’re licensed and following proper handling procedures, which matters for a product like insulin that needs to be shipped cold.
Which Insulin Your Vet Prescribes Affects Where You Can Buy It
Three insulins are commonly used in cats, and each has different availability:
- ProZinc (protamine zinc insulin) is FDA-approved for cats and dogs. It’s a veterinary product concentrated at 40 units per milliliter (U-40). You’ll find it at vet clinics, online pet pharmacies, and some retail pharmacies that carry veterinary medications.
- Vetsulin (porcine insulin) is also FDA-approved for cats and dogs, also U-40 concentration. Similar availability to ProZinc: vet clinics and online pet pharmacies are the most reliable sources.
- Lantus (glargine) is a human insulin used off-label in cats. It’s U-100 concentration. Because it’s a human product, every retail pharmacy stocks it, which gives you the most shopping options and often the lowest price. Many veterinary specialists favor glargine in cats because of its longer duration of action, typically lasting 12 to 24 hours per dose.
Getting the Right Syringes
This is where many cat owners make a costly mistake. Insulin syringes come in two concentrations, and using the wrong one means giving the wrong dose.
ProZinc and Vetsulin are U-40 insulins, meaning 40 units per milliliter. They require U-40 syringes, which have a red cap. These are less common at human pharmacies because people don’t use U-40 insulin. Your best bet is ordering them from the same place you buy the insulin, whether that’s your vet or an online pet pharmacy.
Lantus is a U-100 insulin, meaning 100 units per milliliter. It uses U-100 syringes with an orange cap. These are the standard syringes available at any pharmacy. They’re inexpensive and easy to find.
If you accidentally use a U-100 syringe with a U-40 insulin, you’ll give your cat less than half the intended dose. The reverse, using a U-40 syringe with U-100 insulin, could deliver a dangerously high dose. Always match the syringe to the insulin concentration, and if you’re ever unsure, ask your vet or pharmacist before injecting.
Comparing Prices Before You Buy
Insulin is an ongoing expense for as long as your cat needs it, which in many cases is the rest of their life. A few phone calls can save you hundreds of dollars a year. Call your vet’s office, one or two nearby retail pharmacies, and check an online pet pharmacy for the specific product your vet prescribed. Ask for the price of a 10 mL vial.
For Lantus, the price gap between vet clinics and retail pharmacies can be dramatic. In the CBC News comparison, the cheapest pharmacy price was less than half the most expensive vet clinic price for the exact same vial. ProZinc and Vetsulin pricing tends to be more uniform since fewer retailers carry them, but online pet pharmacies still frequently undercut vet office prices.
Keep in mind that opened insulin vials have a limited shelf life, usually 28 to 42 days depending on the product, even when refrigerated. If your cat uses a small amount per day, some of the vial may go to waste. Your vet can help you estimate how long a vial will last at your cat’s dose so you can calculate the true monthly cost.