Safety

Allergy drop side effects: what’s normal, and when to get help

Most reactions to allergy drops are an itchy mouth in the first few weeks. A few are not. This page covers both: what to expect, what the research says about how often each happens, and exactly when to stop, call your clinician or call 911.

Short answer

Most reactions to sublingual allergy drops are mild and stay in the mouth: itching or tingling of the mouth, lips or throat, slight swelling under the tongue, or an upset stomach, usually in the first weeks and fading within minutes to an hour. Across 26 trials of 7,827 patients on sublingual immunotherapy, about 41% had local side effects, about 1% had a reaction beyond the mouth, and 0.13% had anaphylaxis (Janz 2024, PMID 38840522). Serious reactions are rare, but they happen: trouble breathing, throat tightness, a hoarse voice, widespread hives, fainting or repeated vomiting after a dose means using epinephrine if you have it and calling 911. Do not start drops with severe or uncontrolled asthma or during pregnancy, and hold your dose when your mouth is injured or your asthma is flaring.

Written by Dr. Chet Tharpe, MD · Medically reviewed by Dr. Neeta Ogden, MD, FACAAI · Last reviewed September 2026 · Last verified: September 28, 2026

How common

What the trials show

The most complete estimate comes from a 2024 meta-analysis of 26 prospective trials: 7,827 patients and more than 2.7 million doses of single-allergen sublingual immunotherapy, over an average of 11.5 months.

of patients had a local side effect, mostly in the mouth or throat: 40.8%of patients had a local side effect, mostly in the mouth or throat
had a systemic reaction — symptoms beyond the mouth: 1.09%had a systemic reaction — symptoms beyond the mouth
had anaphylaxis: rare, but it happens: 0.13%had anaphylaxis: rare, but it happens
stopped treatment because of side effects: 4.3%stopped treatment because of side effects

Janz TA et al. Exploring side effects of sublingual immunotherapy: a systematic review and meta-analysis. Ear Nose Throat J 2024 (PMID 38840522). The trials studied single-allergen products; multi-allergen drops were not included.

Normal or not

Expected reactions and warning signs

In the grass tablet trials, itching in the mouth affected 26.7% of patients against 3.5% on placebo, throat irritation 22.6%, ear itching 12.5% and mouth swelling 11.1% (Grastek prescribing information). Liquid drops cause the same kinds of local reaction.

What you notice	What it usually means	What to do
Itching or tingling of the mouth, lips, tongue or throat; itchy ears	A common local reaction, most often in the first weeks, lasting minutes to an hour	Keep dosing as prescribed. Tell your clinician if it is getting worse or lasts beyond the first weeks.
Mild swelling under the tongue or of the lips; a mild sore throat	A local reaction	Tell your clinician before the next dose; the dose may be adjusted.
Upset stomach, nausea or mild stomach ache after dosing	Usually a local reaction to swallowed allergen	Tell your clinician if it happens more than once.
Hives or itching away from the mouth, sneezing fits, itchy swollen eyes	A systemic reaction — symptoms beyond the mouth	Do not take the next dose until you have spoken to your clinician.
Trouble swallowing, food sticking, chest pain or heartburn that keeps coming back	Can be eosinophilic esophagitis, reported with sublingual immunotherapy	Stop dosing and contact your clinician.
Wheezing, throat tightness, hoarse voice, trouble breathing or swallowing, lightheadedness or fainting, repeated vomiting, or widespread hives with any of these	Possible anaphylaxis	Use epinephrine if you have it and call 911. Do not wait to see if it passes.

Adapted from the FDA prescribing information for sublingual tablets (Grastek) and the 2023 anaphylaxis practice parameter. Your own prescriber’s instructions come first.

Real-world data

What the 2,897-patient Curex study found, and what it cannot tell you

A 2026 study in Frontiers in Allergy followed 2,897 adults treated with personalized sublingual drops through Curex between 2020 and 2025 (Tharpe 2026). Adverse events were infrequent and mostly mild: grade I reactions were recorded in 11.7% of patients, and no anaphylaxis or eosinophilic esophagitis was reported.

Read those numbers with their limits. The study was retrospective and single-arm, with no comparison group. It included only patients with at least 12 months of follow-up, so people who stopped early — including anyone who stopped because of a reaction — are not counted. Several authors work for Curex (the statistics were done by an outside firm). And it studied adults only.

No anaphylaxis in one cohort does not mean drops cannot cause anaphylaxis. Anaphylaxis has been reported with sublingual immunotherapy in clinical trials (Janz 2024), and every FDA-approved sublingual tablet carries a boxed warning for severe allergic reactions. Sublingual treatment has a lower rate of systemic reactions than allergy shots, which is why it can be taken at home — lower is not zero.

Holding a dose

When to skip a dose and check with your clinician

Pause and ask before your next dose if any of these apply. Never double a dose to catch up.

Your mouth is sore or injured. Mouth ulcers, thrush, bleeding gums, a tooth extraction or oral surgery: hold until the mouth has healed (Grastek label).
Your asthma is flaring. Wheezing, a worse cough at night, or needing your rescue inhaler more than usual: hold, and treat the asthma first. Repeated flares are a reason to reconsider treatment.
You had a reaction beyond your mouth. Hives, eye swelling, sneezing fits, stomach cramps or anything systemic after a dose: do not take the next one until you have spoken to your clinician.
You are acutely ill. A stomach bug, a high fever or a bad chest infection: many protocols pause until you recover. Ask what yours says.
You missed several days. Ask how to restart. After a longer gap the dose is often stepped back down.
Something changed. A new pregnancy, a new heart or blood-pressure medicine (especially a beta-blocker), or a new diagnosis: tell your clinician before your next dose.

Emergency

When to use epinephrine and call 911

Anaphylaxis is a sudden reaction that affects breathing, circulation or more than one part of the body at once. After a dose, treat any of these as an emergency: throat tightness, a hoarse voice or trouble swallowing; wheezing, repeated coughing or shortness of breath; lightheadedness, fainting or a weak pulse; swelling of the tongue or lips together with any other symptom; or widespread hives with vomiting, cramps or breathing symptoms.

Use epinephrine first, then call 911. If you have been prescribed an epinephrine auto-injector, use it in the outer thigh straight away, call 911, and lie down with your legs raised (or sit up if you are struggling to breathe). Epinephrine is the first-line treatment for anaphylaxis; antihistamines and inhalers do not treat it (2023 anaphylaxis practice parameter). If you have no epinephrine, call 911 immediately. Afterwards, tell your prescriber before taking another dose.

The FDA-approved sublingual tablets require the prescriber to provide an epinephrine auto-injector. For personalized drops, ask your clinician whether you should carry one, and keep it with you if so.

Before you start

Who should not start allergy drops, or should be seen in person first

Severe, unstable or uncontrolled asthma. A contraindication for the FDA-approved sublingual tablets (Grastek label) and a reason for an in-person evaluation before any immunotherapy.
A past severe reaction to immunotherapy. Any severe systemic or severe local reaction to shots, tablets or drops.
Eosinophilic esophagitis. A history of it is a contraindication for the sublingual tablets.
Pregnancy. Do not start immunotherapy during pregnancy. If you become pregnant while already on a maintenance dose, your clinician decides whether to continue — usually without increasing the dose (Cox 2011; WAO 2013).
Beta-blockers or significant heart disease. They can make a severe reaction harder to survive or treat; the tablet labels flag both.
A history of anaphylaxis, a suspected food or drug allergy, or a young child. Start with an in-person allergist evaluation.

Anyone with a history of anaphylaxis, severe or poorly controlled asthma, a suspected food or drug allergy, a young child, or someone who is pregnant should be evaluated by an allergist in person before starting any at-home immunotherapy.

Help and reporting

How to reach a clinician, and how to report a reaction

For anything that is not an emergency, contact the clinician who prescribed your drops. Curex patients reach their clinician by message or video visit through their Curex account; if you use another provider, use the route they gave you. In an emergency, call 911 first — never wait for a message reply.

Anyone can report a side effect to the FDA through MedWatch, online or by phone at 1-800-FDA-1088. Reports from patients count; you do not need a doctor to file one. It also helps to tell your prescriber and the pharmacy that filled the prescription.

One practical note: Curex drops need no refrigeration. They are stable for 14 days at 80–100°F and for 48 hours above 100°F, so a bottle left in a warm car or a delayed delivery is not by itself a safety problem.

Regulation

How allergy drops are regulated

Personalized allergy drops are compounded and prescribed off-label, made from FDA-approved allergenic extracts, the same as in allergy shots; off-label does not mean unsafe or experimental. A small number of single-allergen sublingual tablets are FDA-approved. Side effects of either can be reported to MedWatch.

Regulatory record

Personalized allergy drops, for environmental or food allergy, are made from FDA-approved allergenic extracts and prescribed off-label — a long-standing, legitimate practice that applies to every drops provider, not only Curex. Only a few single-allergen sublingual tablets are FDA-approved.

Has the FDA written to Curex about allergy drops? Once, in 2021: an untitled letter about how the drops were marketed. Curex changed its website, responded in April 2021, and has had no FDA correspondence about allergy drops since.

Does the 2025 FDA warning letter concern allergy drops? No. The September 2025 warning letter concerned marketing language for compounded GLP-1 weight-loss products; Curex made the requested changes.

Every letter and response: Curex and the FDA. The short version: Is Curex legit?

❓Frequently Asked Questions

Itching or tingling of the mouth, lips, tongue or throat, itchy ears, slight swelling under the tongue, and sometimes an upset stomach. They are most common in the first weeks and usually fade within minutes to an hour. In a meta-analysis of 26 trials, about 41% of patients had a local side effect (Janz 2024, PMID 38840522).

Yes, rarely. In the same meta-analysis, 0.13% of patients had anaphylaxis. Sublingual treatment has a lower rate of systemic reactions than allergy shots, which is why it is taken at home, but the risk is not zero. Trouble breathing, throat tightness, a hoarse voice, fainting or widespread hives after a dose means epinephrine if you have it and a call to 911.

Hold your dose and contact your clinician if your mouth is injured or sore, your asthma is flaring, you had a reaction beyond your mouth, you are acutely ill, you have trouble swallowing or recurring chest pain, or you become pregnant. Stop and call 911 for any sign of anaphylaxis.

Do not start allergy drops or any immunotherapy during pregnancy. If you become pregnant while already on a stable maintenance dose, tell your clinician straight away; they decide whether to continue, usually without increasing the dose.

People with severe, unstable or uncontrolled asthma, a past severe reaction to immunotherapy, or eosinophilic esophagitis should not start without specialist advice, and people taking beta-blockers need a careful review. Anyone with a history of anaphylaxis, a suspected food or drug allergy, or a young child should be evaluated in person first.

Adverse events were infrequent and mostly mild (grade I in 11.7% of patients) and no anaphylaxis was reported (Frontiers in Allergy 2026, PMID 42358593). The study was retrospective, had no comparison group, counted only patients with at least a year of follow-up, and was written by Curex clinicians, so it cannot show that drops never cause anaphylaxis.

Tell your prescriber first. Anyone can also report a side effect to the FDA through MedWatch at fda.gov/medwatch or by calling 1-800-FDA-1088; patient reports are accepted.

If you experience sudden difficulty breathing, throat swelling, or other signs of anaphylaxis, call 911. A prescribed epinephrine auto-injector is the first-line treatment — not antihistamines.

This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about a medical condition. Content reviewed by board-certified allergists at Curex.

Curex provides personalized sublingual immunotherapy and publishes this page. It is general information, not a substitute for your prescriber’s instructions. In an emergency, call 911.

Sources and record

Where the facts come from

Sources

Last verified September 28, 2026. Last updated September 28, 2026 · next scheduled review December 2026.

Change log

September 28, 2026 — Published: allergy drops side effects and reactions — trial frequencies (Janz 2024), the 2,897-patient Curex cohort with its limits, when to hold a dose, when to use epinephrine and call 911, who should not start, pregnancy, and MedWatch reporting. Author Dr. Chet Tharpe, MD; medical reviewer Dr. Neeta Ogden, MD.