What Is the Most Painful Shot to Get?

No single shot holds the undisputed title of “most painful,” because injection pain depends on a tangle of factors: what’s in the syringe, where it goes, how deep the needle reaches, and how your own nervous system processes the experience. That said, a few injections have earned genuinely fearsome reputations among patients and clinicians alike. Intramuscular penicillin G benzathine (the syphilis treatment often called Bicillin), the newer recombinant shingles vaccine, and injections directly into joints or the eye consistently rank among the most dreaded. Understanding why certain shots hurt so much more than others turns out to be surprisingly complex.

What Makes One Injection Hurt More Than Another

The pain you feel from any shot is really a sum of several inputs hitting your nervous system at once. The needle punctures the skin (which is packed with pain-sensing nerve endings), then the fluid flowing in stretches the tissue, and the chemical properties of the solution itself can irritate or inflame. Each of these layers contributes independently, and the worst-offender shots tend to pile up problems across all of them.

The chemistry of the injected solution matters more than most people realize. Solutions that sit far from the body’s natural pH or osmolality essentially sting the tissue on contact. Research on intravenous anesthetic agents found that pain kicked in when osmolality exceeded about 1.0 osmol/kg during a slow infusion, and acidic solutions with a pH below 4 or alkaline solutions above 11 reliably caused pain.¹ For subcutaneous drugs, the general recommendation is to keep formulations isotonic (around 300 mOsm/kg) and as close to physiological pH as possible to minimize irritation.² Shots that violate these thresholds can burn or ache from the moment the fluid enters the tissue.

Interestingly, the viscosity of the fluid plays a counterintuitive role. A study testing subcutaneous injections at different viscosities found that thicker solutions actually produced less perceived pain than thin ones, with pain scores averaging about 12.6 mm on a visual analog scale for high-viscosity fluid versus 22.1 mm for low-viscosity fluid.³ The same study found that volume and injection speed had no meaningful effect on pain. So the common assumption that a big, slow push hurts less than a fast one doesn’t hold up well for subcutaneous shots.

The Shots with the Worst Reputations

Ask nurses which injection makes patients wince the most, and penicillin G benzathine will come up quickly. This thick, oily intramuscular antibiotic is the standard treatment for syphilis, and its formulation is essentially designed for slow, sustained release, which means a viscous suspension gets forced into deep muscle tissue. The injection itself is painful enough that researchers have tested combined strategies (including lidocaine mixing, warming, and site selection) to bring down pain scores, with some success at the 30-minute mark after injection but little improvement in the immediate sting.⁴ Patients frequently describe a deep, throbbing ache that lingers well beyond the injection itself, and the formation of hard lumps (induration) at the site is common.

The recombinant zoster vaccine (Shingrix), given to prevent shingles, is another strong contender. In clinical trial data, about 78% of people who received the vaccine reported injection-site pain, and roughly 6.4% rated it as severe (grade 3, meaning pain significant enough to interfere with daily activities). That compares to just under 11% reporting any pain in the placebo group. Beyond the injection site, nearly half of recipients experienced muscle aches and fatigue.⁵ The culprit is largely the vaccine’s potent adjuvant system, which deliberately provokes a strong immune response. That immune kick is what makes the vaccine effective, but it also explains why so many people feel lousy for a couple of days afterward.

Rabies post-exposure treatment deserves a mention too, not because any single needle stick is uniquely painful, but because the protocol involves infiltrating rabies immunoglobulin directly into and around bite wounds. The volume required depends on wound size, ranging from about 1 mL for small wounds to 5 mL for larger ones, and injecting fluid into already-damaged tissue is inherently painful.⁶ The old reputation of rabies shots as excruciating comes partly from a previous era when the vaccine was injected into the abdomen, but the wound-infiltration step remains genuinely uncomfortable.

Where the Needle Goes Changes Everything

Skin, muscle, joints, and the eye all have very different nerve densities and tissue types, and these differences dramatically shape the pain experience. Intradermal injections (just under the skin’s surface) tend to produce sharp, intense initial pain because the skin’s outermost layers are densely packed with sensory nerve endings. Research comparing intradermal and intramuscular capsaicin injections found that the intradermal route produced more intense pain in the first minute, but intramuscular injections led to pain that lasted longer and was more likely to radiate to other areas.⁷ So the “worst” route depends partly on whether you define pain by peak intensity or by how long it drags on.

Joint injections occupy their own category of discomfort. Glenohumeral (shoulder) joint injections, used for conditions like frozen shoulder or arthritis, cause transient pain during or after the procedure in roughly 6.7% of cases. When a post-injection flare occurs, the pain typically lasts 24 to 48 hours and results from a brief inflammatory reaction to the steroid crystals in the solution.⁸ Knee and other large-joint injections follow a similar pattern. The initial needle entry isn’t always terrible, but the pressure and inflammatory flare can make the following day or two miserable.

Intravitreal injections (directly into the eye) sound horrifying, and many patients dread them intensely. The reality, though, is somewhat better than the anticipation. One clinical trial found mean pain scores across all intravitreal injections were 1.82 on a 0-to-10 scale, with scores ranging from 0 to 7.⁹ Topical anesthesia (numbing drops) does most of the heavy lifting here. The discomfort patients report is often more about the psychological distress of watching a needle approach their eye than about the physical sensation itself. That said, anxiety plays a real role in amplifying the experience: one study found that for every 1-point increase on an anxiety scale, intravitreal injection pain scores rose by about 0.10 points.¹⁰ That might sound small per point, but anxiety scores can vary widely across patients, making the cumulative effect meaningful.

Your Brain’s Role in How Much a Shot Hurts

The physical stimulus is only part of the story. Your nervous system actively amplifies or dampens pain signals based on what you expect to feel, what you see, and how anxious you are. A study using a clever “rubber hand” setup showed that when participants watched a needle prick a hand they perceived as their own, they rated the unpleasantness of an electrical stimulus as higher compared to watching a cotton swab touch the hand. The actual physical stimulus was the same in both conditions; only the visual context changed.¹¹ This helps explain why needle-phobic people sometimes experience pain that seems disproportionate to the physical event.

Device design has caught up with this insight. A systematic review of subcutaneous injection devices found that autoinjectors, pen injectors, and other devices that keep the needle hidden from view consistently reduced both anxiety and perceived pain compared to conventional syringes. People who were already anxious about needles especially preferred designs where they never had to see the needle at all.¹² In the TOUCH trial, which compared an autoinjector pen to a standard prefilled syringe for adalimumab (a biologic drug for autoimmune conditions), about 77% of patients found the pen less painful, and roughly 89% preferred it overall.¹³ The drug and needle were the same; only the delivery experience changed.

Who Feels Injection Pain More

Pain perception isn’t uniform across people, and two well-studied variables are sex and age. Across multiple vaccine types, including hepatitis A, hepatitis B, tetanus-containing vaccines, anthrax, and influenza, women consistently report higher rates of injection-site pain than men.¹⁴ The reasons are genuinely multifactorial: laboratory pain studies show that women tend to have lower pain thresholds and that sex hormones modulate pain sensitivity, with thresholds varying across the menstrual cycle.¹⁵ Experimental injection of glutamate into jaw muscles, for instance, produced significantly greater peak pain and longer-lasting pain in women than in men.¹⁶ Social conditioning and reporting differences probably contribute too, but the biological component is well established.

Age has a clearer effect in children than in adults. A study of children undergoing venipuncture found that both the perceived intensity and unpleasantness of needle pain decreased steadily with increasing age, with the correlation between those two ratings running at about 0.78.¹⁷ In hospitalized adults, the picture flattens out: procedural pain intensity doesn’t appear to differ much between younger and older adults, though younger patients tend to show more distress and emotional reactivity.¹⁸ So a five-year-old getting a vaccine genuinely perceives the pain differently than a teenager getting the same shot, but a 30-year-old and a 70-year-old are likely on more equal footing physically, even if they cope with it differently.

Practical Ways to Reduce the Pain

If you’re facing a shot you know will be painful, a few evidence-backed strategies can help. For injections involving local anesthesia (dental procedures, wound repair, minor surgeries), the technique of the person giving the shot matters enormously. Slow injection of lidocaine hurts significantly less than rapid injection, and in at least one study the speed of administration had a bigger impact on pain than whether the lidocaine had been pH-buffered.¹⁹ Buffering lidocaine with sodium bicarbonate does help too, with patients preferring buffered over unbuffered lidocaine at a ratio of about 3 to 1.²⁰ When clinicians combine small-gauge needles, slow injection, proper buffering, and warmed solution, it is possible to reduce the experience to little more than the initial prick.²¹

Vibration devices, which press a buzzing gadget against the skin near the injection site, have become popular as a drug-free pain reducer. The theory relies on gate control: vibration stimulates large sensory nerve fibers that can partially block pain signals from reaching the brain. Results in the research are mixed, though. A randomized trial in children receiving vaccines found that vibration alone did not significantly reduce pain.²² In adults, the picture is somewhat more positive: a trial of upper-extremity injections found that vibration reduced post-injection pain sensation in the area around the injection site,²³ and another study in adults with type 2 diabetes found that both a vibration device and a ShotBlocker (a small plastic disc with blunt pressure points) significantly lowered pain scores during insulin injections.²⁴ The takeaway is that vibration probably helps adults more reliably than children, and it works better as part of a bundle of strategies rather than as a standalone fix.

For vaccines specifically, distraction (conversation, deep breathing, looking away) and topical numbing creams applied beforehand remain the simplest approaches. They won’t eliminate the pain of something like Shingrix, but they can take the edge off. And if you’re getting multiple shots in one visit, asking the clinician to give the least painful one first can reduce overall distress, since the order of injections has been shown to influence perceived pain in studies of sequential injections.²⁰

How Needle Technology Has Changed the Experience

If the question of the “most painful shot” had been asked a few decades ago, the honest answer would have been that nearly all of them hurt more than they do now. Early insulin syringes used needles ranging from 19 to 26 mm in length that had to be manually sharpened against a whetstone and sterilized by boiling. Modern pen needles are as short as 4 mm and as thin as 34 gauge, with engineered tip geometry and lubricated coatings that dramatically reduce insertion pain.²⁵ That century of refinement is one reason why routine shots like insulin and most vaccines register as a mild pinch for the majority of people. The shots that still hurt badly tend to be ones where the formulation itself is the problem (thick suspensions, irritating pH), or where the anatomy makes gentleness difficult (joints, wounds, the eye). Hardware improvements have solved a lot of the needle-related pain; the remaining pain frontier is largely chemical and anatomical.

There’s also growing interest in needle-free delivery systems, including jet injectors, microneedle patches, and oral or nasal alternatives for vaccines. These technologies are at various stages of development and adoption. Microneedle patches, which use arrays of tiny projections that barely penetrate the outermost skin layer, have shown promise for painless vaccine delivery in clinical testing, though none have reached widespread routine use. If these approaches eventually replace conventional needles for the highest-pain injections, the question of which shot hurts most could become largely historical.