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Grastek Side Effects

Generic Name: timothy grass pollen allergen extract

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

In Summary

Common side effects of Grastek include: mouth edema, throat irritation, and pruritus of ear. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to timothy grass pollen allergen extract: sublingual tablet

In addition to its needed effects, some unwanted effects may be caused by timothy grass pollen allergen extract (the active ingredient contained in Grastek). In the event that any of these side effects do occur, they may require medical attention.

Major Side Effects

You should check with your doctor immediately if any of these side effects occur when taking timothy grass pollen allergen extract:

More common:
  • Itching of the ears, mouth, or tongue
  • numbness or tingling feeling around the mouth
  • sore throat
  • swelling of the mouth
Less common:
  • Chest discomfort
  • difficult or labored breathing
  • difficulty swallowing
  • hives or welts, itching, or skin rash
  • redness, swelling, or soreness of the tongue or in the mouth
  • runny nose
  • swelling of the lips
  • tightness in the chest
Incidence not known:
  • Cough
  • dizziness
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
  • fast heartbeat
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • sweating
  • unusual tiredness or weakness

Minor Side Effects

Some of the side effects that can occur with timothy grass pollen allergen extract may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

Less common:
  • Acid or sour stomach
  • dry throat
  • headache
  • heartburn
  • nausea
Incidence not known:
  • Diarrhea
  • drowsiness

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 & Company Inc, Whitehouse Station, NJ.

Not all side effects for Grastek may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.