Lidocaine injections in the back typically provide 1 to 2 hours of numbing at the injection site, though meaningful pain relief often extends well beyond that. In studies tracking patients after back injections, the median duration of significant pain relief ranged from 6 to 9 hours, with some people experiencing relief for a day or longer. The wide range depends on where the injection is placed, whether other medications are mixed in, and what’s causing your pain.
The Numbing Effect vs. Pain Relief
There’s an important distinction between how long lidocaine actively numbs tissue and how long you might feel better afterward. The drug itself works as a local anesthetic for roughly 1 to 2 hours when injected into soft tissue. It kicks in within 10 to 20 minutes and then gradually wears off. That’s the pharmacological window, the period when the drug is chemically blocking nerve signals.
But pain relief can outlast the numbing. A multicenter study published in Interventional Pain Medicine found that patients receiving lidocaine injections near spinal nerves reported a median of 6 to 9 hours of at least 80% pain reduction, depending on how relief was measured. Some patients in the study experienced relief lasting 48 hours. About two-thirds of people who responded to the injection had meaningful relief lasting at least 2 hours, while roughly a third felt pain return in under 2 hours. This wide spread is normal and reflects differences in individual anatomy, the specific pain source, and how inflamed the area is.
How Epinephrine Extends the Effect
Your doctor may use lidocaine mixed with epinephrine (sometimes called adrenaline), which constricts blood vessels around the injection site. This slows down how quickly your body absorbs and clears the lidocaine, effectively doubling the anesthetic window. Plain lidocaine provides 1 to 2 hours of local numbing, while the epinephrine combination extends that to 2 to 4 hours. Whether your injection includes epinephrine depends on the procedure and the location of the injection, so it’s worth asking beforehand if you want to know what to expect.
Common Types of Back Injections Using Lidocaine
Medial Branch Blocks
These target the small nerves that carry pain signals from your facet joints, the bony connections between vertebrae. Lidocaine medial branch blocks are often diagnostic, meaning their main purpose is to confirm where your pain is coming from rather than to treat it long-term. If the injection reduces your pain by more than 50%, that tells your doctor the facet joint is likely the source. The short duration of lidocaine is actually useful here: a clear, time-limited window of relief helps pinpoint the problem. If the block works, you may be a candidate for a longer-lasting procedure like radiofrequency ablation, which can provide months of relief.
Trigger Point Injections
For muscular back pain, lidocaine is sometimes injected directly into tight, knotted areas of muscle called trigger points. The numbing effect lasts the standard 1 to 2 hours, but the mechanical action of the needle itself can release the muscle knot and provide relief that lasts days or weeks. In these cases, lidocaine serves partly as a pain-management tool during the procedure rather than the sole source of lasting relief.
Epidural Steroid Injections
When lidocaine is part of an epidural injection, it’s usually combined with a steroid. The lidocaine provides immediate short-term numbing while the steroid works on inflammation over the following days. You may feel significant relief within hours from the lidocaine, then a gap period where pain returns before the steroid takes full effect (typically 2 to 7 days later). The steroid component can provide weeks to months of relief for conditions like herniated discs or spinal stenosis.
Why Duration Varies So Much
Several factors influence how long your relief lasts. Blood flow to the injection area matters: regions with more blood supply clear the drug faster. The concentration and volume of lidocaine used also play a role, as does your individual metabolism. People with higher body fat percentages may process the drug differently since lidocaine distributes into fatty tissue. The underlying condition matters too. If inflammation is the primary driver of your pain and the injection happens to calm it down mechanically, you could feel better for longer than the drug’s active window would predict.
Your body weight determines how much lidocaine can be safely used. The standard maximum is 4.5 milligrams per kilogram of body weight without epinephrine, or up to 7 milligrams per kilogram with it. For back injections, the actual doses used are typically well below these limits since the target areas are small and precise.
What to Expect After the Injection
You’ll likely feel the area go numb within 10 to 20 minutes. During this window, you might notice that movements or positions that normally hurt feel dramatically better. This is the information your doctor is looking for if the injection is diagnostic. Keep mental notes (or write them down) about how much relief you get and when the pain starts returning, since this helps guide next steps in your treatment.
As the lidocaine wears off, pain typically returns gradually rather than all at once. Some soreness at the injection site itself is common for a day or two. If lidocaine was paired with a steroid, don’t judge the procedure’s success based on the first 24 to 48 hours. The steroid needs time to reduce inflammation, and you may not feel its full benefit for up to a week.
If your injection was purely diagnostic and the short-term relief confirmed the pain source, your doctor will likely discuss longer-lasting options. A successful lidocaine block, even one that only lasts a few hours, opens the door to targeted treatments that can provide months of relief.