An unopened vial of testosterone cypionate lasts 24 months from the date of manufacture when stored at room temperature. Once you puncture the stopper with a needle, the clock changes: a multi-dose vial should be used within 28 days. Those two timelines, the manufacturer’s expiration date and the 28-day after-opening window, are the numbers that matter most.
Unopened Shelf Life: 24 Months
The FDA sets the expiration period for commercially manufactured testosterone cypionate at 24 months from the date of manufacture. This applies when the vial is stored between 59°F and 77°F (15°C to 25°C), with brief temperature swings acceptable down to 36°F or up to 86°F. The vial should also be kept out of direct light. That expiration date printed on the box or vial label reflects this 24-month window, and it’s based on stability testing the manufacturer submits to the FDA.
There’s no published data showing exactly how fast the medication loses potency after that date. The expiration doesn’t mean the testosterone instantly becomes useless or dangerous on day one past the label. But without stability data beyond 24 months, there’s no guarantee the concentration is still what the label says it is, which means your dose could be unpredictably weaker.
After You Open It: The 28-Day Rule
Once a needle punctures the rubber stopper of a multi-dose vial, the sterile seal is broken. The Joint Commission and standard pharmacy guidelines require that opened multi-dose vials be discarded within 28 days, unless the manufacturer specifies a different timeframe. You should write the discard date (not just the date opened) directly on the vial so there’s no guesswork later.
Testosterone cypionate does contain a preservative, benzyl alcohol, at a concentration of about 20 mg per mL. This helps inhibit bacterial growth between uses. But “inhibit” is not the same as “prevent indefinitely.” Each time you insert a needle, you introduce a small contamination risk. The 28-day limit exists because preservative effectiveness has practical limits, and the risk of injecting contaminated oil into muscle tissue is serious enough that the conservative timeline makes sense.
If the 28-day window expires before you’ve used the full vial, you should discard what’s left. The same applies if the manufacturer’s printed expiration date arrives before the 28 days are up. Whichever date comes first wins.
Compounded Vials Have Shorter Dates
If your testosterone cypionate comes from a compounding pharmacy rather than a commercial manufacturer like Pfizer, the rules are more conservative. Compounded sterile preparations are assigned a “beyond-use date” rather than a standard expiration date. These dates are typically shorter because compounding pharmacies don’t conduct the same rigorous, long-term stability testing that large manufacturers perform under FDA oversight.
Your compounded vial’s label will show its specific beyond-use date. Follow that date even if it seems short compared to what you’ve seen on commercial products. The pharmacist who compounded it assigned that date based on the available evidence for that specific formulation, carrier oil, and preparation method.
Storage Mistakes That Shorten Shelf Life
The most common storage error is refrigerating the vial. Testosterone cypionate is a highly concentrated solution (the 200 mg/mL version is actually supersaturated), and cold temperatures cause crystals to form in the oil. This doesn’t necessarily ruin the medication. Warming the vial in your hands or under warm water and shaking it gently will usually redissolve the crystals. But repeated temperature cycling between cold and warm environments can stress the solution and isn’t ideal for long-term stability.
Keep the vial at room temperature, ideally between 68°F and 77°F, in a drawer or cabinet away from sunlight. Avoid storing it in a bathroom where humidity and temperature fluctuate, or in a car where heat can spike well above 86°F.
How to Tell If Something Is Wrong
Normal testosterone cypionate is a clear to slightly yellow oil. The exact shade varies depending on the carrier oil: cottonseed oil tends to be a light amber, while grapeseed oil can appear nearly clear. Some batch-to-batch color variation is normal and doesn’t indicate a problem.
What you should watch for is particulate matter floating in the solution that doesn’t dissolve with gentle warming, a dramatically darker color than when you first opened the vial, or cloudiness that persists after the vial has been at room temperature for several hours. Crystals that form from cold storage look different from contamination. They’re typically small, uniform, and dissolve with warmth. If you see anything that doesn’t resolve with gentle warming, don’t use the vial.
Practical Timeline for Most Users
A standard multi-dose vial of testosterone cypionate contains either 1 mL or 10 mL of solution. For someone on a typical replacement protocol of 100 to 200 mg per week, a 1 mL vial at 200 mg/mL holds one or two doses, so you’ll likely use it well within 28 days. A 10 mL vial holds enough for roughly 10 to 20 weeks of treatment depending on your dose, which means the 28-day after-opening rule becomes the limiting factor long before the vial runs out.
In practice, many people using 10 mL vials at home continue past 28 days. The preservative does provide some protection, and the oil-based solution is inherently less hospitable to bacteria than water-based medications. But the 28-day guideline exists for a reason, and the safest approach is to follow it. If your prescription volume and dose don’t align well with the vial size, talk to your prescriber about getting a vial size that minimizes waste.