Is a Spinal Tap Dangerous? Risks and Side Effects

A lumbar puncture, commonly called a spinal tap, is one of the safest invasive procedures in medicine, though it is not entirely without risk. Large studies consistently report overall complication rates in the range of roughly 8 to 10 percent, but the vast majority of those complications are mild and self-limiting, primarily headaches. Serious complications like bleeding or infection are rare enough that they show up in fractions of a percent. The procedure’s reputation as something frightening owes more to the dramatic-sounding name and the sensitive location than to any actual pattern of harm.

How Often Do Complications Actually Happen

The best way to gauge the real risk of a spinal tap is to look at what happens across hundreds or thousands of procedures. An Australian hospital study reviewing over 500 lumbar punctures found complications in about 10 percent of cases, but the vast majority of those, roughly 9 in 10, were classified as minor. Post-dural puncture headache accounted for most of them.¹ A separate large-cohort study of lumbar punctures performed by a dedicated medicine procedure service found a major complication rate of just 0.1 percent, with minor complications at about 8 percent.²

Those numbers tell a clear story: the chance of something going seriously wrong is small, but you should expect some possibility of a manageable aftereffect, usually a headache. A quality-improvement initiative at a Norwegian university hospital demonstrated that with careful technique and standardized protocols, complication rates can be driven down dramatically, from about 10 percent to under 1 percent, sustained over years.³ The takeaway is that how the procedure is performed matters at least as much as whether it is performed.

Post-Dural Puncture Headache

If there is one side effect you are likely to hear about, it is the post-dural puncture headache. This is the single most common complication and the reason most people feel lousy after a spinal tap. It typically starts within a day or two of the procedure and has a distinctive quality: it gets worse when you sit up or stand and improves when you lie flat.

The underlying mechanism involves the small hole left in the membrane surrounding the spinal cord. Cerebrospinal fluid can leak out through that hole faster than the body replaces it, causing a drop in pressure inside the skull. That pressure drop pulls on pain-sensitive structures in the brain and triggers compensatory widening of blood vessels, both of which contribute to what can be a throbbing, debilitating headache.⁴ For most people the headache resolves on its own within a few days with rest, fluids, and over-the-counter pain relief.

When the headache is severe or does not improve, the standard treatment is an epidural blood patch. A small amount of your own blood, typically 15 to 20 milliliters, is injected into the epidural space near the puncture site. The blood clots and seals the leak, and the resulting pressure boost is more sustained than what you would get from saline or other fluids. Serious complications from the blood patch itself are exceptionally rare, and it is considered the gold standard for persistent post-puncture headache.⁵

The Bed Rest Myth

One of the most persistent pieces of advice people receive after a spinal tap is to lie flat for hours, sometimes the whole day, to prevent a headache. It sounds intuitive. But a systematic review pooling multiple randomized trials found that prolonged bed rest after a lumbar puncture does not reduce the risk of headache compared to getting up and moving around soon after the procedure. In fact, in the group of patients who had spinal anesthesia, shorter bed rest appeared to do slightly better.⁶

This does not mean you should run a marathon afterward. If lying down makes you feel better, by all means do it. But forcing yourself to stay flat for a set number of hours out of the belief that it is medically protective is not supported by the evidence. Many hospitals have updated their protocols accordingly, though patients still get told otherwise with surprising frequency.

Bleeding After a Spinal Tap

A small amount of bleeding at the puncture site is normal and harmless. The concern that worries clinicians is a spinal hematoma, a collection of blood that forms in the spinal canal and could compress the nerves. This is genuinely serious but also genuinely uncommon. A large study of nearly 60,000 patients found that spinal hematoma occurred within 30 days in about 0.2 percent of patients without a bleeding disorder and at a similar rate, about 0.23 percent, in patients who did have a coagulopathy. Even among patients with progressively worse clotting abnormalities, there was no clear pattern of increasing hematoma risk.⁷

That finding might surprise you, because conventional wisdom holds that blood thinners make a spinal tap meaningfully more dangerous. A registry-based study using propensity-score matching found that anticoagulant use did not significantly increase the odds of epidural hematoma and actually showed a statistically lower odds of subdural hematoma. Antiplatelet use showed a trend toward higher epidural-hematoma odds, but the result was not statistically significant.⁸ The clinical reality is more nuanced than a blanket “blood thinners make it dangerous,” and doctors weigh the urgency of the procedure against the patient’s specific clotting status before deciding how to proceed.

Infection Risk

Introducing a needle into the spinal canal creates a potential pathway for bacteria, which is why sterile technique is critical. Iatrogenic meningitis, meaning meningitis caused by the procedure itself, is rare but carries high morbidity and mortality when it does occur.⁹ The emphasis there is on “preventable”: proper skin disinfection and aseptic technique are the main defenses, and lapses in those basics account for most reported cases.

Retrospective estimates put the rate of infectious complications from spinal and epidural needlework in the range of 0 to 0.04 percent. The primary routes of contamination are droplet transmission from the healthcare provider or patient and bacteria from inadequately cleaned skin at the puncture site. Non-compliance with skin disinfection guidelines has been specifically linked to cases where mouth-dwelling bacteria turned up in the cerebrospinal fluid, a telltale sign that the operator was talking over the sterile field without a mask.¹⁰ This is a strong argument for wearing a face mask during the procedure, a practice that is now standard at most institutions but was not always.

When a Spinal Tap Should Not Be Done

There are situations where performing a lumbar puncture would create a genuinely life-threatening risk. The most important is when a patient has a mass or swelling inside the skull that is shifting brain tissue around. Removing cerebrospinal fluid from below the brain in that scenario can cause brain herniation, where the brain is forced downward through the opening at the base of the skull. This is the single most feared complication of lumbar puncture and can be fatal.

Consensus guidelines list the following as contraindications:

Intracranial mass with mass effect: any space-occupying lesion that is displacing brain tissue, especially in the back of the skull.
Abnormal intracranial pressure: conditions like Arnold-Chiari malformation or other causes of dangerously elevated pressure.
Severe coagulopathy: uncorrected bleeding disorders or active anticoagulant therapy that cannot be safely paused.
Local skin infection: infected skin at the planned puncture site, which could introduce bacteria directly.
Spinal abnormalities: congenital or acquired structural problems that make safe needle placement impossible.¹¹

When meningitis is suspected and there is concern about increased intracranial pressure, doctors typically order a CT scan of the head before the procedure. But a normal CT scan does not guarantee safety. Clinical signs suggesting the brain is under pressure, such as altered consciousness, abnormal eye movements, or rapidly worsening neurological symptoms, are actually better predictors of herniation risk than imaging alone.¹² In those situations, doctors will start antibiotics immediately and delay or skip the lumbar puncture rather than risk a catastrophic outcome.

Rare but Real Complications

Beyond headache, bleeding, and infection, a handful of uncommon complications are worth knowing about. One that occasionally follows a severe post-dural puncture headache is cranial nerve palsy, most often affecting the sixth cranial nerve, which controls outward eye movement. When spinal fluid pressure drops significantly and stays low, the resulting traction on cranial nerves can temporarily impair their function, leading to double vision.

A documented case involved a patient who developed a sixth nerve palsy five days after an epidural for labor analgesia. She experienced double vision in all directions of gaze. After conservative treatment failed to fully resolve the headache and nerve symptoms, she received a CT-guided epidural blood patch with 20 milliliters of her own blood. Within 24 hours her headache resolved completely, and over the next two weeks the double vision gradually disappeared as the nerve recovered.¹³ Cases like these are alarming when they happen but tend to resolve fully, especially with timely treatment of the underlying pressure problem.

Other rare aftereffects include temporary back pain or leg numbness at the puncture site, and in extremely rare cases, an epidermoid cyst can form years later if skin cells are inadvertently carried into the spinal canal by the needle. These are textbook curiosities more than genuine clinical concerns for any individual patient.

Ultrasound Guidance and the Skill Factor

One of the biggest variables in how safe and comfortable a spinal tap is has nothing to do with the patient’s anatomy or medical history. It is who is holding the needle and what tools they are using. The traditional approach relies on feeling for landmarks on the spine by hand, which works fine in slim patients with normal anatomy but becomes difficult in people who are overweight or have spine changes from aging or surgery.

Ultrasound guidance has made a meaningful difference. In a study comparing ultrasound-guided lumbar punctures to the conventional approach in overweight patients, the ultrasound group had a success rate of about 93 percent versus 68 percent for the standard method, required fewer needle insertions, and took roughly half the time. Patients in the ultrasound group also reported lower pain levels.¹⁴

In children, the picture is more mixed. A meta-analysis of ultrasound-assisted lumbar puncture in pediatric patients found that for infants specifically, the ultrasound group had a meaningfully higher first-attempt success rate. But in older children, the advantage was not statistically significant, likely because landmark-based technique works well enough in kids with simpler anatomy.¹⁵ Fewer needle attempts generally means less pain, less bleeding, and a faster procedure, so the practical benefit extends beyond just “did they get the fluid.”

Therapeutic Lumbar Punctures and Repeat Procedures

Most people think of a spinal tap as a one-time diagnostic test, used to check cerebrospinal fluid for signs of infection, inflammation, or bleeding. But lumbar punctures are also used therapeutically. Patients with conditions like idiopathic intracranial hypertension may need periodic spinal fluid removal to relieve pressure. People with spinal muscular atrophy who receive intrathecal drug injections, such as nusinersen, undergo lumbar punctures repeatedly over the course of years.

A study of CT-guided lumbar punctures for nusinersen delivery in spinal muscular atrophy patients reported a technical success rate of about 98 percent. Complications occurred in roughly 1 percent of procedures and were limited to transient pain and two hematomas. Patients who had spinal fusion hardware required slightly longer procedures and received somewhat higher radiation doses from the CT guidance, but their success and complication rates were comparable.¹⁶ For patients who need repeated access to the spinal canal, this kind of data is reassuring: the risk does not appear to compound in a way that makes ongoing treatment impractical.

Reducing Pain During the Procedure

The needle going in is the part people dread, and the good news is that local anesthesia makes it far more manageable than the imagination suggests. Most adults receive an injection of lidocaine at the puncture site before the spinal needle is introduced. The lidocaine injection itself stings briefly, but after it takes effect the deeper needle should produce pressure more than sharp pain.

In infants, who cannot be coached through the experience, researchers have explored needle-free jet injection of lidocaine to numb the skin before the lumbar puncture needle goes in. A randomized trial found that infants who received jet-injected lidocaine had significantly lower pain scores at needle insertion and cried for a shorter duration compared to those who received a saline placebo.¹⁷ For older children and adults, the standard lidocaine injection remains effective and widely used. Anxiety management, including clear communication from the clinician about what each step will feel like, plays a surprisingly large role in how patients remember the experience afterward.

What the Operator Does That You Cannot See

Much of what determines your outcome is invisible to you as a patient. The choice of needle gauge and tip design, the use of imaging guidance, whether the clinician wears a mask, the speed of the procedure, and the experience level of the person performing it all influence complication rates in ways the research supports. Dedicated procedure teams consistently achieve better success rates and lower complication rates than general clinicians performing occasional lumbar punctures, which is one reason larger hospitals have been moving toward specialized procedure services for this kind of work.

If you have a choice in where and by whom your lumbar puncture is performed, asking whether the facility uses ultrasound guidance and whether the clinician does the procedure regularly are reasonable questions. These are not guarantees against complications, but they shift the odds in your favor. The Norwegian quality-improvement study that drove complications below 1 percent did so primarily through checklists, standardized needle selection, and operator training, not through any exotic technology.³ Process discipline, not cutting-edge gear, made the difference.