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

For people with allergic asthma, medications like inhalers only mask the problem. They help you breathe today, but they don’t fix what’s causing the reaction in the first place. That’s where allergen immunotherapy comes in. It’s the only treatment that actually changes how your immune system responds to allergens like house dust mites, grass pollen, or tree pollen. And right now, you have two main options: allergy shots (subcutaneous immunotherapy) and SLIT tablets (sublingual immunotherapy). One requires a clinic visit. The other you can take at home. But which one is better for your asthma? Let’s cut through the noise.

How Allergen Immunotherapy Actually Works

Think of your immune system like an overprotective guard who mistakes harmless pollen for a dangerous intruder. Allergen immunotherapy trains that guard to stop overreacting. It does this by giving you tiny, controlled doses of the allergen you’re sensitive to-over months, then years. Your body learns it’s not a threat. That’s why this isn’t just another symptom blocker. It’s disease-modifying. Studies show that after 3 to 5 years of treatment, many people still have less asthma, even after stopping.

And it’s not theoretical. A 2024 study tracking over 14,000 patients found that those on immunotherapy had fewer asthma attacks and used less medication for nearly a decade after starting treatment. Another study showed a 20% drop in lower respiratory infections needing antibiotics among people who completed SLIT. That’s not just fewer inhalers-it’s fewer doctor visits, fewer sick days, fewer emergency trips.

Shots: The Classic Approach

Allergy shots have been around since 1911. They’re injected under the skin, usually in the arm. The process has two phases. First, a build-up phase: you get an injection once a week for about 3 to 6 months. Then, a maintenance phase: you switch to monthly shots, usually for 3 to 5 years. That’s around 50 visits total. You have to wait 30 minutes after each shot because there’s a small risk of a systemic reaction-like swelling, trouble breathing, or low blood pressure. That’s why clinics require supervision.

But here’s the trade-off: shots have proven effectiveness. A 1999 study of 36 patients with dust mite allergies showed clear improvements in both asthma and rhinitis symptoms after 18 months of shots. More recent data confirms that for many, especially those with multiple allergies or severe asthma, shots still deliver stronger symptom control than SLIT tablets. It’s not just about reducing wheezing-it’s about lowering your reliance on steroids. One trial showed SCIT users cut their daily inhaled corticosteroid dose by 45% on average.

SLIT Tablets: The Home-Based Alternative

SLIT tablets, like ACARIZAX for house dust mites, are placed under the tongue and held there for 1 to 2 minutes before swallowing. No needles. No clinic visits after the first dose. After your doctor gives you the first tablet and watches you for 30 minutes to make sure there’s no reaction, you can take the rest at home-every day. That’s the big draw: convenience.

But it’s not just about ease. A 2024 study found that people using the 6 SQ-HDM dose of SLIT reduced their daily steroid inhaler use by 42% compared to placebo. That’s nearly half. And unlike shots, SLIT has a much lower risk of serious reactions. Most side effects are mild: an itchy mouth, swollen lips, or a sore throat. These usually fade within a few weeks. Adherence is higher too-75% to 80% of SLIT users stick with it, compared to 60% to 65% for shots. Why? Because life doesn’t stop for clinic appointments. Work, kids, travel, weather-all get in the way of weekly visits.

Comparing Effectiveness: What the Data Really Shows

Let’s be clear: neither option works for everyone. Both require that your asthma is triggered by a specific, testable allergen. If your asthma flares from pollution, cold air, or stress, immunotherapy won’t help. You need skin prick tests or blood tests to confirm you’re allergic to dust mites, grass, or tree pollen.

Here’s how they stack up:

Older studies said shots were better for asthma. But newer real-world data from Europe shows SLIT delivers nearly the same benefit-especially for house dust mite allergies, which are the most common trigger for year-round asthma. The difference now isn’t effectiveness. It’s lifestyle.

Who Should Choose What?

Here’s the practical breakdown:

• Choose shots if: You’re allergic to multiple allergens (like dust mites + grass + cats), your asthma is moderate to severe, or you’ve tried SLIT and didn’t respond. Shots have more flexibility in dosing and can cover more allergens at once.
• Choose SLIT tablets if: You’re mainly sensitive to one allergen (like house dust mites), you have mild-to-moderate asthma, you hate needles, or your schedule doesn’t allow weekly clinic visits. SLIT is also better for kids and teens who want independence.

But there’s a catch. Neither works if your asthma is out of control. If you’re on GINA Step 4 or 5 treatment (multiple inhalers, oral steroids, frequent ER visits), immunotherapy isn’t the place to start. You need to stabilize first. Then, talk to your allergist about adding AIT as a long-term solution.

Real-World Challenges

Even the best treatment fails if you don’t stick with it. Both require 3 to 5 years. That’s longer than most people expect. The benefits don’t show up overnight. You might feel a little better after 6 months, but the real payoff comes after year three. That’s why adherence is everything.

SLIT users often quit because they forget. Daily pills are easy to skip. Shots fail because people miss appointments. One UK study found that patients who set phone reminders were 3 times more likely to complete treatment. If you’re considering either, build a routine. Link it to brushing your teeth. Set calendar alerts. Tell a friend. Make it non-negotiable.

Cost is another factor. In the UK, SLIT tablets are often covered by the NHS for eligible patients. Shots may require private care or specialist referral. In the US, insurance coverage varies wildly. Check what’s covered before you start.

What’s Next?

The field is evolving. New formulations are being tested-some with adjuvants to boost effectiveness, others with shorter treatment times. There’s also growing evidence that starting AIT in children with allergic rhinitis can prevent asthma from developing later. Nine out of ten studies now show this protective effect.

But the biggest barrier isn’t science. It’s access. In Europe, 60-70% of allergists offer SLIT. In the US, it’s closer to 10-15%. That’s changing, slowly. More clinics are adopting standardized tablets. More guidelines now recommend SLIT as a first-line option for dust mite asthma.

If you’re tired of relying on inhalers, if you’re tired of flares that ruin your weekends, if you want to reduce your medication burden for good-then allergen immunotherapy is worth exploring. Not as a miracle cure, but as a long-term strategy that actually rewires your immune system. And whether you choose shots or tablets, the goal is the same: to live with less asthma, not just manage it.

Next Steps

If you’re considering immunotherapy, start with testing. Ask your GP for a referral to an allergy specialist. Get skin prick or blood tests to confirm which allergens trigger your asthma. Don’t assume it’s dust mites-many people are allergic to multiple things.

Once you know your triggers, ask: “Is there an approved immunotherapy for this allergen?” If yes, ask: “Which option-shots or tablets-fits my life better?” Consider your schedule, your fear of needles, your ability to remember daily pills, and your asthma severity.

There’s no one-size-fits-all. But for the right person, immunotherapy can mean years of fewer attacks, fewer pills, and more freedom. It’s not a quick fix. But it’s the only treatment that might change your asthma forever.