Allergen Immunotherapy for Asthma: Shots vs. SLIT Tablets - What Works Best?

If you’ve been struggling with asthma triggered by pollen, dust mites, or pet dander, and your inhaler isn’t doing enough, you might have heard about allergen immunotherapy. It’s not just another medication-it’s the only treatment that actually changes how your immune system reacts to allergens. And when it comes to choosing between allergy shots and SLIT tablets, the decision isn’t just about convenience. It’s about long-term control, safety, and whether you’re willing to stick with a treatment that takes years to work.

What Is Allergen Immunotherapy, Really?

Allergen immunotherapy (AIT) isn’t about masking symptoms. It’s about rewiring your body’s overreaction to harmless things like dust mites or grass pollen. For decades, doctors treated asthma with inhalers and antihistamines-fine for flare-ups, but they don’t stop the root cause. AIT does. By slowly exposing you to tiny, controlled doses of the allergen you’re sensitive to, your immune system learns not to overreact. Think of it like training your body to ignore the trigger instead of panicking every time it shows up.

This isn’t new. Back in 1911, a doctor named Leonard Noon gave his hay fever patient a pollen injection. It worked. Today, we have two main ways to deliver that same idea: shots under the skin (SCIT) or tablets held under the tongue (SLIT). Both are backed by decades of research and are recommended in European and global asthma guidelines for patients with allergic asthma that doesn’t fully respond to standard meds.

How Allergy Shots (SCIT) Work

Allergy shots mean regular trips to the clinic. You start with weekly injections, usually for 3 to 6 months, then move to monthly shots for 3 to 5 years. Each dose contains a tiny amount of the allergen-like house dust mite extract-that your body is sensitive to. Over time, your immune system gets used to it.

The big advantage? SCIT has a long track record of reducing asthma symptoms, lowering the need for inhalers, and even preventing asthma from getting worse. A 1999 study of 36 patients with dust mite allergies showed clear improvements in both nasal and asthma symptoms after shots. Even today, many allergists consider SCIT the gold standard for strong, broad allergen control.

But here’s the catch: you have to show up. Fifty-plus visits over three years. That’s hard if you work late, have kids, or live far from an allergy clinic. And while most reactions are mild-redness or swelling at the injection site-there’s a small risk of a serious allergic reaction. That’s why you have to wait 30 minutes after each shot. It’s safe, but it’s not easy.

How SLIT Tablets Work

SLIT tablets-like ACARIZAX for dust mites or GRAZAX for grass pollen-are taken daily at home. You place the tablet under your tongue, hold it there for two minutes, then swallow. No needles. No clinic visits after the first dose.

The first dose is always given in a doctor’s office because, like shots, there’s a small risk of a systemic reaction. But after that? You’re on your own. And that’s why adherence is higher. Studies show 75-80% of people stick with SLIT compared to 60-65% for shots. Convenience matters.

And the results? Strong. A 2024 study found that patients using the highest dose of HDM SLIT (6 SQ-HDM) reduced their daily inhaled corticosteroid use by 42%-that’s almost half the medication. Placebo users only dropped 15%. Better yet, SLIT users had 20% fewer lower respiratory infections needing antibiotics after treatment ended. That’s not just symptom relief-it’s fewer sick days, fewer ER visits, fewer antibiotics.

Shots vs. Tablets: The Real Differences

Let’s cut through the noise. Both work. But they’re not the same.

• Effectiveness: SCIT has slightly stronger evidence for asthma symptom control in older studies. But newer, larger real-world data shows SLIT matches or even beats shots in reducing medication use and exacerbations.
• Convenience: SLIT wins by a mile. One tablet a day at home vs. weekly clinic visits. If you’re busy, SLIT is easier to stick with.
• Safety: SLIT has fewer serious reactions. Most side effects are mild: itchy mouth or throat, which usually fades after a few weeks. Shots carry a slightly higher risk of anaphylaxis, though it’s rare.
• Duration: Both need 3-5 years. No shortcuts. If you quit early, you won’t get the long-term benefit.
• Cost: SLIT may cost more upfront per month, but you save on travel, time off work, and fewer steroid inhalers. Over five years, many patients end up ahead financially.

One key point: neither works if your asthma is severe (GINA step 4 or 5) or if your triggers aren’t allergic. If your asthma flares from cold air, exercise, or stress-not pollen or dust-AIT won’t help. You need to know your trigger. That means skin testing or a blood test for specific IgE antibodies first.

Who Should Choose Which?

Let’s say you’re a parent juggling two kids and a full-time job. You can’t take time off every week for shots. SLIT tablets fit into your routine. You can take them while brushing your teeth or eating breakfast. You’re more likely to stick with it-and that’s what matters.

Or maybe you’re allergic to multiple things-dust mites, cat dander, and ragweed. SCIT can target several allergens in one injection. SLIT tablets are allergen-specific. Right now, only dust mite and grass pollen tablets are approved in the UK and EU. If you’re allergic to cats or mold, shots are your only option.

And what about kids? Evidence shows AIT can prevent asthma from developing in children with allergic rhinitis. One review of nine studies found kids on AIT had a significantly lower chance of developing asthma later. That’s huge. SLIT is often preferred for children because it’s needle-free and easier to manage at home.

What You Won’t Hear from Your Doctor

Most doctors will tell you AIT works. But they won’t always tell you how hard it is to get.

In the UK and Europe, SLIT tablets are widely available and covered by the NHS in many areas. In the US? Not so much. Only a handful of SLIT products are FDA-approved. Many allergists there still default to shots because they’ve been doing it for decades.

Also, AIT isn’t a quick fix. You won’t feel better in a month. It takes 6-12 months to start seeing changes. The real payoff comes after year two or three-when your inhaler use drops, your cough fades, and you stop waking up gasping at night. But you have to stick with it.

And here’s something rarely discussed: not all allergen extracts are equal. The dose matters. The 6 SQ-HDM dose for dust mites is proven. Lower doses? Less reliable. Make sure you’re getting the right dose-not just any tablet or shot.

What Happens After You Stop?

This is the magic part. Most asthma medications only work while you take them. Stop the inhaler? Symptoms come back. Stop antihistamines? Sneezing returns.

With AIT, the effect lasts. Studies show benefits continue for years after you stop treatment. One 9-year follow-up found AIT patients still had fewer asthma attacks and lower medication use than those who never had it. That’s not just symptom control-it’s disease modification.

It’s like getting vaccinated against your allergens. Your immune system remembers. It learns not to attack.

Is It Worth It?

If you’ve been on asthma meds for years and still feel like you’re barely holding on, AIT might be your best shot at real freedom. It’s not for everyone. But if you have confirmed allergic asthma, and you’re willing to commit to 3-5 years, it’s one of the most powerful tools we have.

Shots give you a little more flexibility if you’re allergic to multiple triggers. But SLIT tablets are easier, safer, and just as effective for dust mite or grass pollen allergies. For most people with mild-to-moderate asthma, SLIT is the smarter, more practical choice.

The bottom line? Don’t just treat your asthma. Fix it.

Frequently Asked Questions

Next Steps If You’re Considering AIT

Start with an allergy test. Skin prick or blood test for IgE antibodies to dust mites, grass, or other triggers. If the results point to a clear allergen, talk to your GP about a referral to an allergy specialist.

Ask: “Is my asthma allergic? Is my trigger covered by an approved SLIT tablet? What’s the evidence for this treatment in my case?” Don’t accept a one-size-fits-all answer. Your treatment should match your life, your allergies, and your goals.

If you’re tired of relying on inhalers, and your asthma is tied to a specific allergen, AIT might be the first real step toward breathing easier-without medication.