Why Does Testosterone Crystallise?

Why does testosterone crystallise? It’s a question we get asked a lot, so we’ve put together an article to explain the different factors that contribute to crystal formation in testosterone preparations, including structural differences between compounds such as testosterone cypionate and enanthate.

We’ll dig into the role esters play, plus external factors like supersaturation, temperature changes, UV light exposure, and storage techniques. You’ll learn how medical TRT practitioners handle crystals in your testosterone medication to ensure optimal results.

Structural Differences in Testosterone Compounds

Testosterone Cypionate such as Nebido (available on the Alphagenix Alpha Plan) and Testosterone Enanthateis are injectable forms of testosterone commonly used in TRT. They differ structurally via the esters attached to their respective oxygen atoms on the steroid molecule. These contribute to their varying tendencies towards crystallisation.

Comparing Testosterone Cypionate and Enanthate structures

In Testosterone Cypionate, an eight-carbon chain is attached to the 17-beta hydroxyl group. Testosterone Enanthate has a seven-carbon chain. It might seem like a small difference but it greatly influences each compound’s solubility and rate of release into the bloodstream after injection.

  • Cypionate: Eight-carbon chain – higher tendency for crystallization
  • Enanthate: Seven-carbon chain – lower tendency for crystallization

The role of esters in crystal formation

Esters play an important role in determining whether or not crystals will form in testosterone. The longer carbon chains found within cypionate molecules tend to promote greater levels of supersaturation – that’s a state where greater than normal levels of solute dissolves

That then makes it more likely that crystals will form if the storage temperature isn’t stable of the testosterone is handled improperly.

Factors Contributing to Crystallisation

The following influence the crystallisation process;


Supersaturation, occurs when a solution contains more solute than it is able to dissolve at equilibrium. As the concentration of dissolved testosterone increases beyond this saturation point, crystals may begin to form.


Varying temperatures can be a cause of crystal growth in testosterone solutions. When exposed to colder environments or rapid temperature changes (i.e. storing it near air conditioners or refrigerators), the solubility of testosterone decreases significantly, which promotes crystalline precipitation. Maintaining consistent room temperature storage conditions reduces this risk.

UV Light Exposure

Exposure to ultraviolet (UV) light has been shown to cause degradation and subsequent crystallisation within some injectable medications like Testosterone Cypionate (source). Storing vials away from direct sunlight or other sources of bright light will help protect their integrity over time.


  • Maintain suitable storage conditions by keeping vials at room temperature and away from heaters, air con or refrigerators.
  • Ensure solutions remain below their saturation point to prevent supersaturation and crystal formation.
  • Avoid exposing vials to direct sunlight or other sources of UV light

Dealing with Crystals in Testosterone Solutions

Crystals formed within testosterone solutions aren’t harmful in themselves, but they need to be delat with properly before administration. Manufacturers recommend warming up cypionate solutions and shaking them vigorously so that any present crystals dissolve back into suspension again.

Warm Vials

To warm up a testosterone vial, simply hold it between your hands for a few minutes or place it in a small container filled with warm water (but not hot water, or you’ll end up in hot water too). Gentle heat will help dissolve existing crystals without compromising the integrity of the solution. Avoid applying direct heat sources.

Shaking Techniques

  • Gently agitate : Hold the vial firmly between your fingers and gently roll it back and forth to create some visible movement inside. This should be done for about 30 seconds to one minute until the crystals have dissolved.
  • Vigorous shaking : If the gentle approach doesn’t work, try holding the vial securely in one hand while using your other hand to shake it vigorously up and down for another minute or two.

Inspect each vial visually prior to use – even those stored under optimal conditions – as crystallisation can still occur over time despite the best of intentions.

Best Storage Strategies

Proper storage techniques play an essential role in preventing or minimising crystal formation within testosterone cypionate solution. The guidelines will stand you in good stead;

Avoid Excessive Agitation During Storage/Transportation

Keep the vials upright and handle them gently to minimise any disturbance that could trigger crystallisation.

Insulate Vials While Traveling – Store Inside Hand Luggage Instead of Checked Baggage

When traveling with testosterone injections by air, store the vials inside your hand luggage, as this area typically experiences less temperature fluctuation compared to the hold on airplanes

Store Away from Windowsills or Other Sources of Bright Light

  • Sunlight: Direct exposure to sunlight can cause significant fluctuations in temperature, which we don’t want. Store your testosterone vials away from windowsills or any areas where they may be exposed directly to sunlight.
  • Bright lights: Artificial lighting sources such as lamps can generate heat and contribute towards changes in temperature if placed too close to stored medication. Be aware of this too.
  • Temperature-controlled environment: Ideally keep your testosterone vials in a temperature-controlled environment, such as a cool and dark cupboard or drawer that maintains consistent temperatures throughout the day.

Injection Preparation Tips

proper injection preparation is crucial to the success of your TRT protocol. Ensure no air enters the vials when drawing up injections. This will help prevent contaminants from entering the solution.

Preventing Air Entry into Vials

To avoid introducing air into the testosterone solution, follow these steps:

  1. Cleanse the area: Thoroughly clean the top of the vial with an alcohol swab before inserting a needle.
  2. Invert and insert: Invert the vial upside down and insert a sterile syringe needle through its rubber stopper. Slowly draw back on the plunger to fill it with testosterone solution without applying excess pressure.
  3. Tap out bubbles: After withdrawing the requisite medication, tap gently on the syringe barrel sides to remove any visible air bubbles that may have formed during this process. Push them out by depressing the plunger slightly until they are gone.

Sterile Environment Maintenance

The following guidelines can be used to ensure a sterile envrionment:

  • Cleanliness is Godliness: Clean your hands using soap and water, or hand sanitiser before handling any equipment
  • Do not touch the needle: If you accidentally touch or contaminate needles during the injection preparation process, discard them immediately and replace them with new ones.
  • Dispose of sharps responsibly: Properly dispose of all sharps, syringes, and other waste materials in a puncture-resistant container to prevent potential hazards.

Solvent Choice

Research has shown that the choice of solvent plays a significant role in determining the properties and behaviour of testosterone crystals.

This section will discuss how different solvents can affect crystal morphology, purity, and solvation state in testosterone solution.

Different Solvents

X-Ray diffraction analysis has shown that testosterone crystallised from octanol exhibits different characteristics compared to those formed using other alcohols like hexanol and decanol (C5-C10).

They tend to be more uniform and exhibit higher purity levels than their counterparts derived from alternative solvents.

Implications for TRT

By choosing a suitable solvent, patients can ensure optimal results throughout their treatment course by minimising issues related to crystal formation or impurities.

  • Remain solvent: Patients should consult with healthcare professionals when deciding on a suitable solvent for dissolving their prescribed form of injectable testosterone. The ideal choice may vary depending on factors such as personal preferences or medical history.
  • Maintaining proper storage conditions: As discussed earlier, temperature fluctuations and exposure to light can contribute significantly towards crystallisation within testosterone solutions.
  • Regular monitoring: Patients should regularly inspect their testosterone solutions for signs of crystallisation or other abnormalities and report any concerns to their healthcare provider promptly.


How long is testosterone stable?

The stability of injectable testosterone depends on its formulation, storage conditions, and expiration date.

Generally, unopened vials can remain stable for up to 2 years if stored properly; however, once opened or mixed with solvents for injection purposes, the shelf life may be shorter depending on factors like contamination risk.

Does injectable testosterone expire?

Yes, injectable testosterone has an expiration date which should be indicated on the product packaging.

It’s important to adhere to this date as expired products may lose potency over time or become contaminated due to degradation of preservatives within the solution.


Understanding why testosterone crystallises is important for men who are undergoing testosterone replacement therapy.

Proper handling of crystals in testosterone solutions, injection preparation tips, and solvent choice can all play a role in ensuring the best results.

If you’re looking to optimise your TRT outcomes and prevent crystal formation from occurring, consider reaching out to AlphaGenix today. Our team specialises in helping men achieve optimal hormonal balance through personalised treatment plans tailored to their unique needs.