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Grastek Side Effects

Generic name: timothy grass pollen allergen extract

Medically reviewed by Last updated on Dec 12, 2022.

Note: This document contains side effect information about timothy grass pollen allergen extract. Some dosage forms listed on this page may not apply to the brand name Grastek.

Applies to timothy grass pollen allergen extract: sublingual tablet.


Sublingual route (Tablet)

Timothy Grass Pollen Allergen Extract can cause life-threatening allergic reactions such as anaphylaxis and severe laryngopharyngeal restriction. Do not administer Timothy Grass Pollen Allergen Extract to patients with severe, unstable or uncontrolled asthma. Observe patients in the office for at least 30 minutes following the initial dose. Prescribe auto-injectable epinephrine, instruct and train patients on its appropriate use, and instruct patients to seek immediate medical care upon its use. Timothy Grass Pollen Allergen Extract may not be suitable for patients with certain underlying medical conditions that may reduce their ability to survive a serious allergic reaction, or in patients who may be unresponsive to epinephrine or inhaled bronchodilators (eg, those taking beta-blockers).

Serious side effects of Grastek

Along with its needed effects, timothy grass pollen allergen extract (the active ingredient contained in Grastek) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking timothy grass pollen allergen extract:

More common

Less common

Incidence not known

Other side effects of Grastek

Some side effects of timothy grass pollen allergen extract may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

Incidence not known

For Healthcare Professionals

Applies to timothy grass pollen allergen extract: sublingual tablet.


The most common side effects were ear pruritus, oral pruritus, tongue pruritus, mouth edema, and throat irritation.[Ref]


Uncommon (0.1% to 1%): Systemic allergic reactions (including anaphylaxis)

Postmarketing reports: Anaphylactic reaction, angioedema[Ref]


Very common (10% or more): Throat irritation (up to 22.6%)

Common (1% to 10%): Pharyngeal edema, dry throat, oropharyngeal pain, nasal discomfort, throat tightness, dyspnea, pharyngeal erythema, cough, nasal congestion, sneezing

Uncommon (0.1% to 1%): Rhinorrhea, dysphonia

Postmarketing reports: Asthma exacerbation, hoarseness, laryngitis, induced asthma exercise, decreased forced expiratory volume, hyperventilation, laryngeal discomfort, decreased oxygen saturation, decreased peak expiratory flow rate, pneumonia, respiratory distress, status asthmaticus, decreased vital capacity, wheezing[Ref]


Common (1% to 10%): Chest discomfort

Postmarketing reports: Chest pressure, increased heart rate, irregular heart rate, hypotension[Ref]


Common (1% to 10%): Pruritus, urticaria

Postmarketing reports: Facial erythema, rash[Ref]


Very common (10% or more): Oral pruritus ( up to 26.7%), Lip pruritus (up to 11.1%), mouth edema ( up to 11.1%)

Common (1% to 10%): Lip pruritus, oral paresthesia, tongue pruritus, lip swelling, swollen tongue, dyspepsia, oral hypoesthesia, nausea, oral discomfort, oral mucosal erythema, lip edema, glossitis, stomatitis, tongue disorder, tongue edema, glossodynia, dysphagia, palatal edema, glossodynia

Uncommon (0.1% to 1%): Abdominal pain, gastroesophageal reflux, mouth swelling, oral/pharyngeal itching

Postmarketing reports: Oral ulceration, ulcerative colitis exacerbation, diarrhea, eosinophilic esophagitis, oral pain, throat pruritus, vomiting[Ref]

Nervous system

Common (1% to 10%): Headache

Postmarketing reports: Altered state of consciousness, difficulty speaking, dizziness, drowsiness, tremor[Ref]


Very common (10% or more): Ear pruritus (up to 12.5%)

Common (1% to 10%): Fatigue

Uncommon (0.1% to 1%): Ear itching

Postmarketing reports: facial edema, sensation of foreign body, neck swelling[Ref]


1. Product Information. Grastek (timothy grass pollen allergen extract). Merck & Co., Inc. 2014.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.