Mastic has an unusually clean safety record in trials, and the European regulator lists 0 known side effects for it. The real risk sits in 1 place, allergy.
It belongs to the same plant family as pistachio and cashew.
Quick Answer: What Are the Side Effects of Mastic Gum?
In trials mastic was well tolerated, and the EMA monograph lists no known undesirable effects and no reported interactions. The main risk is allergy: 13 of 18 people allergic to Mastisol, a surgical adhesive, reacted to gum mastic on patch testing. Mastic is not recommended in pregnancy, breastfeeding or under 18.
Key Takeaways
- The EMA monograph lists 0 known undesirable effects for oral mastic.
- 13 of 18 people allergic to Mastisol adhesive also reacted to mastic.
- Among 250 patch-tested patients without that history, only 1 reacted to it.
- Mastic shares 1 plant family with pistachio, cashew and mango.
- The EMA does not recommend it in pregnancy or under 18.
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What the Trials Recorded
Across the human studies, adverse effects were rare enough that most abstracts report none. Background on the resin itself is in what mastic gum is.
| Trial | Dose and length | Adverse effects reported |
|---|---|---|
| Duodenal ulcer, 1984 | 1 g a day, 2 weeks | No side effects |
| H. pylori pilot, 2010 | Up to 3.15 g a day, 14 days | No serious adverse events |
| Cholesterol, 2016 | 1 g a day, 8 weeks | No gut, liver or kidney events |
| H. pylori add-on, 2026 | With quadruple therapy, 14 days | No increase in adverse effects |
In the 8-week cholesterol trial no gastrointestinal, liver or kidney adverse events were recorded among 156 analysed volunteers.[1]Effects of Chios mastic gum on cholesterol and glucose levels of healthy volunteers: A prospective, randomized, placebo-controlled, pilot study (CHIOS-MASTIHA) — European Journal of Preventive Cardiology (2016) View source The H. pylori rows are covered in full with the eradication numbers.
What the European Regulator Says
The EMA monograph is the most authoritative safety summary available, and it is short.
- Contraindication: Hypersensitivity to mastic.
- Interactions: None reported.
- Undesirable effects: None known.
- Pregnancy and breastfeeding: Not recommended, for lack of data.
- Under 18: Not recommended for oral use.
The monograph also says to see a doctor if dyspepsia symptoms persist beyond 2 weeks.[2]European Union herbal monograph on Pistacia lentiscus L., resina (mastic) — European Medicines Agency View source None reported is not the same as none possible, because few formal interaction studies exist.
Allergy, Where the Real Risk Is
The clearest allergy data comes from an unexpected place: a skin adhesive used after surgery.
- Mastisol: A liquid adhesive containing gum mastic and gum storax.
- In allergic patients: 13 of 18 reacted to gum mastic, 72%.
- In other patients: 1 of 250 reacted, 0.4%.
- Likely culprit: Linalool, a fragrance compound mastic contains.
The same patients often co-reacted with fragrance materials and propolis.[3]Contact Dermatitis From Gum Mastic (Pistacia lentiscus) and Gum Storax (Liquidambar styraciflua) in Mastisol-Allergic Patients — Dermatitis (2021) View source If you have reacted to surgical glue, perfume or propolis, treat mastic with caution.
Rarer still, 2 people developed a severe pustular rash after swallowing mastic essential oil.[4]Acute generalized exanthematous pustulosis induced by the essential oil of Pistacia lentiscus — Clinical and Experimental Dermatology (2012) View source That was the concentrated oil, not the resin, but it is a reason to stop at the first rash.
Pistachio, Cashew and Pine
Mastic belongs to Anacardiaceae, the family that includes pistachio, cashew and mango. Direct cross-reactivity data for mastic itself does not exist.
- Closest evidence: Terebinth, a sister Pistacia species.
- Finding: 96% of 27 pistachio-sensitive children also reacted to terebinth.
- Mastic tested: No, never in that setting.
- Pine: 0 PubMed records on mastic and pine allergy.
The terebinth study recommends avoiding it with pistachio or cashew allergy until tested.[5]Exploring Terebinth Cross-Sensitivity in Individuals with Pistachio Sensitivity — International Archives of Allergy and Immunology (2024) View source With a known pistachio, cashew or tree-resin allergy, the same caution is sensible for mastic.
The Liver Question
It is the most-asked safety question in search results, and the data is reassuring but thin.
- Rats, 13 weeks: Liver weights rose at the top dose of 2% of diet.
- Under the microscope: No treatment-related findings in any organ.
- No-effect level: 0.67% of the diet.
- People, 8 weeks: No liver adverse events at 1 g a day.
The rat study concluded that the heavier livers came without any morphological change.[6]Evaluation of the toxicity of mastic gum with 13 weeks dietary administration to F344 rats — Food and Chemical Toxicology (2007) View source The doses people actually take are summarised in the EMA dose range.
Interactions and Long-Term Use
The main practical interaction is with the reason people take mastic in the first place.
- With H. pylori antibiotics: Used as an add-on in 1 trial, well tolerated.
- With acid blockers: Mastic plus pantoprazole cleared 0 of 13 in 2010.
- Longest human use: Up to 6 months in inflammatory bowel studies.
- Self-care limit: 2 weeks for dyspepsia, per the EMA.
For anyone with H. pylori, the antibiotic comparison matters more than any side effect.
Who Should Not Take It
For most adults the list is short. For these groups the answer is no, or not yet.
- Known allergy: To mastic, Mastisol or related resins.
- Pregnancy and breastfeeding: Not recommended by the EMA.
- Children and teenagers: Not recommended under 18.
- Untreated H. pylori or ulcer: Needs a clinician, not a herb.
Outside those groups, our 1000 mg mastic gum is 1 capsule at the bottom of the EMA range.
Stop and Speak to a Clinician If
- You develop a rash, hives, swelling or itching after starting mastic
- You are allergic to pistachio, cashew, mango, Mastisol adhesive or propolis
- You are pregnant, breastfeeding or under 18
- Your stomach symptoms last more than 2 weeks or keep returning
- You have black stools, vomiting, weight loss or difficulty swallowing
Frequently Asked Questions
What are the downsides of taking mastic gum? +
Allergy is the main 1, especially if you react to Mastisol adhesive. Trials otherwise reported it as well tolerated.
Is mastic gum hard on the liver? +
No human liver harm has been reported. Rats fed 2% of their diet had heavier livers for 13 weeks but no tissue damage.
Who shouldn't take mastic gum? +
People allergic to it, pregnant or breastfeeding women, and anyone under 18. Untreated H. pylori needs a clinician first.
How long is it safe to take mastic gum? +
Human studies ran up to 6 months in bowel disease. For dyspepsia the EMA advises a doctor after 2 weeks of symptoms.
Can mastic gum cause constipation? +
None of the 4 main trials we read reported constipation. If it happens, stop and review the dose with a clinician.
Can you be allergic to mastic gum? +
Yes. 13 of 18 people allergic to Mastisol adhesive reacted to gum mastic on patch testing, against 1 of 250 others.
Does mastic gum interact with medications? +
The EMA reports 0 known interactions, but few studies looked. Tell your prescriber, especially with antibiotics or acid blockers.
Is mastic gum safe during pregnancy? +
Safety has not been established, so the EMA does not recommend it. That applies to all 9 months and to breastfeeding.
Can children take mastic gum? +
The EMA does not recommend oral mastic under 18 years, because there is not enough data.
Is mastic related to pistachio? +
Yes. Both belong to the Anacardiaceae family, and 96% of 27 pistachio-sensitive children reacted to terebinth, a sister species.
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