What Happens If You Hit a Vein While Injecting Testosterone?

When you accidentally nick or puncture a vein during an intramuscular testosterone injection, some of the oil-based solution can slip into your bloodstream and travel to your lungs. This triggers a reaction known as pulmonary oil microembolism, or POME, which typically announces itself through a sudden fit of coughing and sometimes a wave of lightheadedness. The experience can feel alarming, but the vast majority of these episodes pass on their own within minutes, and they are far less common than many self-injectors fear.

How Oil Gets From Your Muscle to Your Lungs

Injectable testosterone is suspended in an oil carrier, usually castor oil or cottonseed oil. The oil is what makes the medication thick and slow to absorb, creating the “depot” effect that releases the hormone gradually over days or weeks. When you inject into muscle tissue, the oil sits in a pocket between muscle fibers and is absorbed locally. But muscle tissue is threaded with blood vessels, and if the needle tip happens to be inside or very near a vein at the moment you push the plunger, a portion of that oil gets introduced directly into venous circulation.

Once in the bloodstream, the oil droplets travel through veins toward the heart and then get pumped into the pulmonary arteries, the small vessels feeding the lungs. Those droplets are large enough to partially obstruct tiny lung capillaries, irritating the surrounding tissue and triggering a reflexive cough.

What POME Actually Feels Like

The hallmark symptom is a sudden dry cough that comes on within seconds to minutes of the injection. This is not a tickle in the throat; people typically describe it as an uncontrollable urge to cough that seems to come from deep in the chest. Oil-based depot injections can cause acute pulmonary reactions characterized primarily by this cough, sometimes accompanied by other symptoms like chest tightness, shortness of breath, faintness, or a metallic taste in the mouth.¹ Some people break into a sweat or feel mildly anxious during the episode, which is understandable given how unexpected the sensation is.

In a postmarketing safety analysis of testosterone undecanoate injections, roughly 95% of reported POME cases showed symptoms within 30 minutes of the injection. Of those where resolution time was tracked, most cleared up within 30 minutes, and the remaining handful resolved by 3 hours. Over 60% of patients required no medical intervention at all.² A broader literature review found that almost all POME cases resolved spontaneously within an hour without treatment.³

So if you are mid-injection or have just finished and you start coughing hard, stop injecting (if you have not already), sit down, and give it a few minutes. For most people, the coughing tapers off and the episode becomes a weird memory. That said, if symptoms worsen, if you feel genuinely unable to breathe, or if chest pain intensifies rather than fading, that is the point to seek emergency care. The line between “uncomfortable but resolving” and “needs medical attention” is whether symptoms are getting better or getting worse over a span of several minutes.

How Often Does This Actually Happen?

This is where the numbers get interesting, because the reported rates vary quite a bit depending on the specific testosterone formulation and how carefully providers were watching for it.

One study tracking 551 weekly intramuscular injections of testosterone ester in 26 men found 8 episodes of sudden cough with faintness, a rate of about 1.5%.⁴ A larger clinical practice study that recorded over 3,000 testosterone undecanoate injections across 347 patients found POME after 56 of those injections, an incidence of roughly 19 per 1,000 injections. About two-thirds of those episodes were mild, though roughly one in five was classified as severe.⁵

Meanwhile, a postmarketing review of testosterone undecanoate (brand name Aveed) that cast a much wider net found only 223 reported POME cases across over 3 million injections, a far lower rate.³ The difference likely reflects underreporting in the real world, where a brief coughing fit after an injection might not make it into a formal adverse event report, while in a clinical study with a nurse standing right there, every cough gets logged.

So the realistic picture is: POME is uncommon but not vanishingly rare. If you inject testosterone regularly over months or years, there is a reasonable chance you will experience at least a mild episode at some point. But the odds of any single injection causing it are low.

Why Some People Get It More Than Once

One curious finding from the clinical practice data is that recurrences happen more often than random chance would predict.⁵ In other words, if you have had a POME episode, you are statistically more likely to have another one with future injections. Researchers are not entirely sure why. It may relate to individual anatomy, like having veins that are positioned particularly close to the typical injection site, or to subtle differences in body composition that affect how the needle interacts with tissue. It could also involve injection technique that varies from person to person. The same study found that the rate did not differ between three experienced nurse injectors, which suggests that the provider’s skill level is not the main variable. Something about the individual patient’s anatomy seems to matter more.

This is worth knowing because if you have experienced a coughing episode before, you can prepare: inject slowly, stay seated, and have someone nearby if possible. It does not mean you need to stop testosterone therapy, but it means POME is a recurring possibility for you rather than a fluke.

When Onset Happens Before the Injection Is Even Finished

A detail that surprises many people is that about 40% of the POME events in one large study began while the injection was still being administered, before the plunger was fully depressed.⁵ This makes sense when you consider that oil entering a vein would reach the lungs within a few heartbeats. If you start coughing partway through injecting, stop immediately. You will have absorbed some of the dose already, and forcing the remaining oil through during a POME episode is both uncomfortable and unnecessary.

When Injection Technique Goes Wrong

In the small number of POME cases serious enough to require an emergency room visit, issues with injection technique or dosing were identified as a likely contributing factor in three out of four cases.² That is a small sample, but it lines up with what clinicians expect: the way you inject matters. Injecting too quickly, using the wrong needle gauge, or choosing a site with more superficial vasculature can all increase the odds that oil ends up somewhere it should not.

Injection speed is probably the most controllable variable. Testosterone in oil is viscous, and the temptation is to push hard on the plunger to get it over with. But a slower, more controlled injection gives the oil time to settle into a depot within muscle tissue rather than being forcefully dispersed into surrounding blood vessels.

Does Aspiration Actually Help?

Aspiration, the old practice of pulling back on the syringe plunger after inserting the needle to check for blood return, was long taught as the standard way to confirm you were not in a vein. The logic was straightforward: if blood flows back into the syringe, you reposition and try again. Many people who inject testosterone were taught this technique and still practice it.

The evidence, however, suggests it does not do much. A meta-analysis looking at aspiration during intramuscular injections found that it increases pain and injection time without reducing complication risk.⁶ International nursing guidelines have moved away from recommending routine aspiration for most intramuscular injections. The reasoning is that at standard injection sites like the vastus lateralis or the ventrogluteal region, there are no large blood vessels that the needle is likely to enter. The small veins that thread through muscle tissue are too small to produce a reliable blood return even if the needle is sitting right in one.

That said, the meta-analysis noted that technique should be individualized based on medication type and patient characteristics. Testosterone undecanoate in particular involves a large volume of thick oil injected deep into the gluteal muscle, which is a different situation from a standard vaccine. Some clinicians still aspirate for testosterone injections specifically, and if your provider recommends it, there is no harm in continuing the practice beyond the small increase in discomfort.

The Z-Track Method and Injection Site Selection

One technique that has clearer evidence behind it is the Z-track method. Instead of inserting the needle straight in, you use your non-dominant hand to pull the skin and underlying tissue to one side before inserting the needle. After injecting, you release the skin, which creates a zigzag path that seals the oil inside the muscle rather than allowing it to track back along the needle path. A study on intramuscular injections found that the Z-track technique reduced drug leakage compared to standard technique.⁷ While that study looked at a different injected medication, the principle applies to any oil-based intramuscular injection: keeping the oil in the muscle and out of the tissue layers closer to the skin and the veins that run through them.

Injection site also plays a role. In the study that tracked 551 testosterone ester injections across three sites, the gluteal muscle had fewer overall complaints and was less prone to bleeding than deltoid or thigh injections, though it was more often associated with pain at the injection site.⁴ The ventrogluteal site, the area on the upper outer portion of the hip, is generally favored for deep intramuscular injections because it has a thick layer of muscle and fewer major blood vessels compared to other sites.

Subcutaneous Injections as a Way Around the Problem

An increasingly popular alternative is subcutaneous injection, where the needle goes into the fat layer just under the skin rather than deep into muscle. The subcutaneous compartment has far fewer blood vessels than muscle tissue, which substantially reduces the chance of introducing oil directly into circulation.⁸

Subcutaneous testosterone uses smaller needles, involves less discomfort, and is easier for self-injection. Research supports it as a safe and effective delivery route for testosterone cypionate and enanthate, the formulations most commonly used for self-administered testosterone replacement therapy and gender-affirming hormone therapy. Not all formulations are suited for subcutaneous use, though. Testosterone undecanoate, which comes in a much larger volume of castor oil, is designed specifically for deep intramuscular injection and is not typically given subcutaneously.

If you are someone who has experienced POME or who is anxious about vein puncture, asking your prescriber about switching to subcutaneous testosterone cypionate or enanthate at more frequent, smaller doses is a reasonable conversation to have.

The Aveed Situation and Why Clinics Are Involved

Testosterone undecanoate, sold as Aveed in the United States, has an unusual regulatory status among testosterone formulations. Because of the POME risk and a smaller risk of anaphylaxis, the FDA required the manufacturer to establish a Risk Evaluation and Mitigation Strategy (REMS) program. This means Aveed must be administered by a healthcare professional in a clinical setting, and the patient must be observed for at least 30 minutes after each injection.⁹ ⁸

This mandatory observation period exists because testosterone undecanoate is injected in a very large volume (3 mL of thick castor oil) deep into the gluteal muscle, which creates a higher probability of oil entering the vasculature compared to the smaller volumes used with testosterone cypionate or enanthate. The 30-minute window aligns neatly with the data showing that nearly all POME events manifest within that time frame. If you are receiving Aveed, you cannot self-administer it, and the in-office observation requirement is non-negotiable.

The other common formulations, testosterone cypionate and testosterone enanthate, do not carry a REMS requirement. They are routinely self-injected at home, though the possibility of POME still exists at a lower rate because of their smaller injection volumes and different oil vehicles.

Self-Injection and Knowing What Is Normal

Many people on testosterone therapy inject at home, whether for hypogonadism treatment or gender-affirming hormone therapy. A narrative review of self-injection experiences among transgender individuals on injectable hormones found that self-injected therapy was generally well tolerated, with injection site reactions being the most commonly reported issue. Those reactions were typically managed while continuing therapy.¹⁰ The review also identified gaps in long-term teaching and assessment of self-injection practices, which is a polite way of saying that many people learn the basics during one clinic visit and then figure out the rest on their own.

If you self-inject, there are a few things worth keeping in mind to distinguish normal from concerning:

Minor bleeding: A small amount of blood at the injection site is common and means you nicked a capillary during the needle stick. It is not the same as injecting into a vein, and a dab of pressure with a cotton ball takes care of it.
Soreness: Post-injection muscle soreness lasting a day or two is normal, especially with oil-based formulations. It does not indicate a complication.
Sudden coughing: A dry cough within minutes of injecting, especially if accompanied by lightheadedness or chest tightness, is the classic POME presentation. Sit down, breathe calmly, and give it time. It will very likely pass.
Prolonged breathing difficulty: If you are still struggling to breathe after 15 to 20 minutes, or if symptoms are clearly getting worse rather than better, call for medical help.

Injecting at a reasonable pace, using the Z-track technique, choosing the ventrogluteal or vastus lateralis site, and not panicking if a mild cough starts are all within your control. The evidence consistently shows that even when POME does occur, it resolves quickly for the overwhelming majority of people. What the evidence also shows is that people who inject regularly over long periods benefit from periodic check-ins with a provider to make sure their technique has not drifted, since small habits can compound over hundreds of injections.

Blood Thinners and Injectable Testosterone

A common concern is whether being on anticoagulant or antiplatelet medication makes intramuscular testosterone injections riskier. One study directly tracked this and found no post-injection hematomas in 269 injections given to men taking blood thinners, including 56 injections where the blood-thinning medication was not withheld beforehand.⁵ That is reassuring data for people who need both testosterone therapy and anticoagulation, a combination that is not unusual in older men being treated for hypogonadism. The standard advice is still to apply firm pressure to the injection site afterward, but the fear of dangerous bleeding from a routine intramuscular injection appears to be overblown based on the clinical data available.

1
PubMed. Pulmonary oil micro-embolism (POME) syndrome: a review and summary of a large case series
2
PubMed Central. Occurrence of Pulmonary Oil Microembolism After Testosterone Undecanoate Injection – Section: Results
3
PubMed. Occurrence of pulmonary oil microembolism (POME) with intramuscular testosterone undecanoate injection: literature review
4
Human Reproduction. Andrology: Tolerability of intramuscular injections of testosterone ester in oil vehicle
5
European Journal of Endocrinology. Complications of injectable testosterone undecanoate in routine clinical practice
6
PubMed. Aspiration in intramuscular injection: a meta-analysis of pain, duration, and clinical outcomes
7
PubMed. The Effect of the Z-Track Technique on Pain and Drug Leakage in Intramuscular Injections
8
The Journal of Clinical Endocrinology & Metabolism. Testosterone Therapy With Subcutaneous Injections: A Safe, Practical, and Reasonable Option
9
PubMed Central. Occurrence of Pulmonary Oil Microembolism After Testosterone Undecanoate Injection – Section: Background
10
Journal of the American Pharmacists Association. Self-injection experiences among transgender people on injectable gender-affirming hormone therapy: A narrative review