A spinal tap, also called a lumbar puncture, is not a dangerous procedure for most people. It’s one of the more common diagnostic tests in medicine, and serious complications are rare. That said, it does carry real side effects, the most common being a headache that affects up to 25% of patients. Understanding what’s likely, what’s rare, and what makes the procedure safer can help you feel more prepared if you or someone you care about needs one.
The Most Common Side Effect: Headache
The side effect most people experience after a spinal tap is a headache caused by spinal fluid leaking through the tiny hole left by the needle. This is called a post-dural puncture headache, and its frequency varies widely depending on the type of needle used and individual patient factors. Rates in studies range from less than 2% to as high as 40%, though Mayo Clinic puts the overall figure at up to 25%.
The headache typically starts within a few hours to two days after the procedure. It tends to feel worse when you’re sitting or standing and improves when you lie flat. It can come with nausea, vomiting, and dizziness. For most people, it resolves on its own within a few days with rest, fluids, and over-the-counter pain relief. In cases where the headache is severe and doesn’t improve, a treatment called an epidural blood patch can seal the leak. This involves injecting a small amount of your own blood near the puncture site, and it’s highly effective.
Back Pain and Nerve Irritation
Some soreness or tenderness at the needle site in your lower back is normal and usually fades within a day or two. Occasionally, the pain radiates down the back of the legs due to brief irritation of a nearby nerve root during the procedure. This is uncomfortable but almost always temporary. Permanent nerve damage from a standard lumbar puncture is exceptionally rare, partly because the needle is inserted below the point where the spinal cord ends, into an area where nerve fibers float freely in fluid and can move aside.
Rare but Serious Risks
The complications that make people most nervous, like infection, bleeding, or brain herniation, are genuinely uncommon. Infection at the puncture site or in the spinal fluid is possible but occurs in a tiny fraction of procedures when proper sterile technique is used. Significant bleeding is a concern primarily for people who have bleeding disorders or are taking blood-thinning medications, which is why your doctor will review your medications and may order blood tests beforehand.
Brain herniation, where a sudden drop in spinal fluid pressure causes brain tissue to shift downward, is the most feared complication. It’s relevant almost exclusively in patients who have elevated pressure inside the skull from a mass like a tumor or abscess. This is why doctors often order a CT scan before performing a lumbar puncture if there’s any suspicion of a space-occupying lesion. When this screening is done properly, the risk of herniation drops to near zero for the general population getting a spinal tap.
Needle Type Makes a Difference
Not all spinal tap needles are the same, and the type used significantly affects your risk of complications. A large analysis published in The Lancet compared newer “atraumatic” needles, which spread tissue fibers apart rather than cutting through them, to conventional cutting needles. The results were striking: headache rates dropped from 11% with conventional needles to 4.2% with atraumatic ones. That’s a 60% reduction in risk.
Atraumatic needles also cut the need for epidural blood patches in half, reduced severe headaches by nearly 60%, and lowered rates of nerve root irritation and even hearing disturbances. Importantly, they worked just as well on the first attempt and didn’t increase failure rates. These benefits held across all patient groups regardless of age, sex, or the reason for the procedure. If you’re scheduled for a spinal tap, it’s reasonable to ask whether an atraumatic needle will be used.
Who Shouldn’t Have a Spinal Tap
There are a few situations where the procedure carries higher risk and may need to be postponed or avoided entirely. The main contraindications include:
- Elevated brain pressure from a mass or lesion, which raises the risk of herniation
- Bleeding disorders or blood-thinning medications, which increase the chance of dangerous bleeding near the spine
- Skin infection at the puncture site, which could introduce bacteria into the spinal fluid
- Spinal epidural abscess, where inserting a needle could spread existing infection
Your medical team screens for all of these before proceeding. If one applies to you, they’ll either treat the underlying issue first or find an alternative way to get the diagnostic information they need.
Why Doctors Order It Despite the Risks
A spinal tap is rarely optional. It’s ordered when no other test can provide the same information, typically to diagnose or rule out conditions where delay could be life-threatening. Meningitis, certain cancers affecting the brain or spinal cord, multiple sclerosis, bleeding around the brain, and abnormal spinal fluid pressure are among the most common reasons. In many of these situations, the risk of not doing the procedure far outweighs the risk of the procedure itself. A missed case of bacterial meningitis, for example, can be fatal within hours.
In some conditions, the spinal tap itself is part of the treatment. Patients with dangerously high spinal fluid pressure may need repeated lumbar punctures to drain excess fluid and prevent neurological damage. Studies in patients with cryptococcal meningitis found that those who received additional therapeutic lumbar punctures had significantly lower mortality rates than those who didn’t.
What Recovery Looks Like
The procedure itself takes about 30 to 45 minutes. You’ll typically be asked to lie on your side with your knees pulled toward your chest, or sometimes to sit and lean forward. A local anesthetic numbs the skin before the needle goes in, so most people feel pressure rather than sharp pain. Afterward, you’ll rest lying down for a period, usually 15 to 30 minutes, while staff monitor you.
Most people can go home the same day. Drinking plenty of fluids and resting for the first 24 hours helps reduce the chance of headache. You’ll want to avoid strenuous activity for a day or two. If a headache does develop and gets worse rather than better over several days, or if you notice fever, increasing pain, numbness, or fluid leaking from the puncture site, those are signs to contact your medical team promptly.