An epidural is a method of delivering pain-relieving medication into the space just outside the membrane that surrounds your spinal cord. A thin catheter is placed in your lower back, allowing a continuous flow of numbing medication to block pain signals before they reach your brain. It’s most commonly associated with childbirth, but epidurals are also used for surgeries and to treat chronic back pain.
How the Epidural Space Works
Your spinal cord sits inside a protective sac made of layered membranes. The epidural space is the narrow gap between the outermost membrane (the dura) and the walls of your spinal canal. It runs the full length of your spine, from the base of your skull down to your tailbone. This space contains the roots of nerve fibers that carry pain signals from your body to your brain.
When medication is injected into the epidural space, it soaks into those nerve roots and blocks their electrical signals. The blocking happens in a specific order: the smallest nerve fibers shut down first, which controls things like blood vessel tone and temperature sensation. Next, the sensory fibers that carry pain and touch go quiet. Finally, if the dose is high enough, the motor fibers that control muscle movement are affected. This is why a well-dosed labor epidural can take away pain while still letting you feel pressure and move your legs to some degree.
What Happens During Placement
You’ll sit upright or lie on your side, curling forward to open the spaces between your vertebrae. The doctor first numbs a small patch of skin on your lower back with a local anesthetic, so you’ll feel pressure but not sharp pain during the rest of the procedure. A specialized needle, typically about 3.5 inches long, is then guided between two vertebrae toward the epidural space. For patients with a larger body frame, longer needles (up to 6 inches) are available.
The doctor finds the epidural space using a technique called “loss of resistance.” As the needle passes through the tough ligaments between the vertebrae, there’s natural resistance against the syringe plunger. The moment the needle tip crosses the final ligament and enters the epidural space, that resistance suddenly drops. On average, the distance from skin to that point is about 4 centimeters, though it varies from person to person. Once the space is confirmed, a thin, flexible catheter is threaded through the needle, the needle is removed, and the catheter is taped to your back. Medication then flows through this catheter for as long as it’s needed.
Epidurals During Labor
Labor epidurals use very dilute concentrations of numbing medication, often combined with a small amount of an opioid pain reliever. The combination allows each drug to be used at a lower dose, which reduces side effects. Most labor epidurals use concentrations around 0.1% for the numbing agent, a dose low enough to dull pain while preserving some sensation and leg strength.
One consistent finding is that epidurals lengthen labor. Research on early epidural placement (before 3 centimeters of cervical dilation) found the second stage of labor, the pushing phase, averaged about 107 minutes compared to 70 minutes without an epidural. The first stage was roughly an hour longer as well. Whether this longer labor leads to more assisted deliveries with forceps or vacuum remains debated. Some studies find a small increase in instrumental delivery rates, while others show no statistically significant difference. Epidurals do not appear to increase the likelihood of cesarean section.
Epidurals for Back and Nerve Pain
Outside the delivery room, epidural steroid injections have been used since the 1950s to treat back and leg pain caused by compressed or irritated spinal nerves. The most common reason is a herniated disc pressing on a nerve root, which causes pain that radiates down the leg (often called sciatica). Other conditions treated this way include spinal stenosis, bone spurs pushing on nerves, and pain that persists after back surgery.
Unlike labor epidurals, steroid injections are a single-shot procedure rather than a continuous infusion. The steroid reduces inflammation around the irritated nerve. Evidence for effectiveness is strongest for herniated disc pain, moderate for spinal stenosis, and weaker for post-surgical back pain. These injections are typically used when physical therapy and oral medications haven’t provided enough relief, and they can be repeated a limited number of times per year.
Common Side Effects
The most frequent side effect is a drop in blood pressure. Epidural medication blocks the sympathetic nerves that help maintain blood vessel tone, causing blood vessels to relax and widen. In pregnant women, this effect is amplified because the uterus already compresses major blood vessels, and pregnancy shifts the nervous system toward higher sympathetic activity, so blocking those signals creates a bigger swing. The result can be lightheadedness, nausea, or feeling faint. Medical teams monitor blood pressure closely and can treat drops quickly with IV fluids or medication to tighten blood vessels.
Other common side effects include itching (especially when opioids are added to the mix), difficulty urinating (a temporary catheter may be placed), and shivering. Some people experience a feeling of heaviness or weakness in the legs, which resolves after the medication wears off. A small number of people notice patchy or one-sided numbness, meaning the block doesn’t spread evenly.
When an Epidural Doesn’t Work
Epidurals don’t always provide complete pain relief. Failure rates in studies range from about 8% to 23%, depending on how “failure” is defined. In one study of 500 labor epidurals, 15.2% met at least one criterion for failure: 8% of women still reported significant pain 45 minutes after placement, 2.2% needed the catheter repositioned, and 0.6% had the procedure abandoned entirely. The reassuring finding is that with active troubleshooting, including adjusting or replacing the catheter, 98.8% of patients ultimately achieved adequate pain relief.
The most common reasons for incomplete relief are a catheter that migrated slightly off-center or one that didn’t advance far enough into the epidural space. If your epidural leaves you with a “window” of pain on one side, letting your care team know early gives them the best chance of fixing it.
Rare but Serious Complications
The most well-known complication is a post-dural puncture headache, which happens when the needle accidentally goes a fraction too deep and punctures the dura membrane. Spinal fluid leaks through the tiny hole, and the resulting drop in fluid pressure around the brain causes a distinctive headache that worsens when you sit or stand and improves when you lie flat. Incidence varies widely depending on needle size, patient age, and technique. In non-obstetric patients, one study found a rate of about 21.7%, though this was with spinal (not epidural) needles, which intentionally puncture the dura. With epidural needles, accidental puncture is less common because the goal is to stop just short of the membrane.
If a post-dural puncture headache develops, it often resolves on its own within a week or two. For persistent or severe cases, a procedure called a blood patch, where a small amount of your own blood is injected near the puncture site to seal the leak, is highly effective. Extremely rare complications include nerve damage, infection, or bleeding in the epidural space, but these occur in fewer than 1 in 10,000 cases with modern techniques.