Cromolyn Side Effects: What's Normal and What's Not

If you've been prescribed Cromolyn Sodium — whether as Gastrocrom or a generic version — it's natural to wonder about side effects. The good news is that Cromolyn is generally considered one of the safest medications for mast cell disorders. It's poorly absorbed into the bloodstream, which means most side effects are mild and related to the digestive system.

Still, it's important to know what to watch for. This guide covers the common side effects, the rare but serious ones, and when you should call your doctor.

What Is Cromolyn?

Cromolyn Sodium is a mast cell stabilizer that prevents mast cells from releasing inflammatory chemicals like histamine. It's FDA-approved for systemic mastocytosis and is also used off-label for mast cell activation syndrome (MCAS). For a full overview of the drug, see our guide on what Cromolyn is and how it's used.

The oral solution form — which is the prescription version most commonly discussed — has very low bioavailability (only about 0.5–2% is absorbed). This is actually a feature, not a bug: it works locally in the gut and has minimal systemic effects.

Common Side Effects

The following side effects are the most frequently reported with Cromolyn Sodium oral solution, based on FDA labeling:

• Headache — one of the most commonly reported side effects
• Diarrhea — can occur especially when starting the medication
• Nausea — usually mild and may improve over time
• Abdominal pain — stomach cramps or discomfort
• Muscle aches (myalgia) — joint or muscle soreness
• Itchiness — mild skin irritation
• Unpleasant taste — the oral solution has a taste some patients find disagreeable
• Skin rash — mild rashes that typically resolve

Most of these side effects are mild and tend to improve within the first week or two of treatment. If you're just starting Cromolyn, give your body a little time to adjust before assuming it's not going to work for you.

Serious Side Effects

Serious side effects with Cromolyn are rare, but they can happen. Contact your doctor right away if you experience any of the following:

• Severe allergic reaction (anaphylaxis) — signs include difficulty breathing, swelling of the face or throat, severe hives, rapid heartbeat, or dizziness. This is very rare but requires immediate emergency care.
• Worsening of symptoms — if your mastocytosis or mast cell symptoms get noticeably worse after starting Cromolyn, tell your doctor.
• Joint pain and swelling — persistent or severe joint inflammation is uncommon but should be evaluated.
• Difficulty swallowing — if you experience trouble swallowing or a feeling that something is stuck in your throat, seek medical attention.

Cromolyn does not carry a boxed warning, which is the most serious type of FDA safety warning. This reflects its overall strong safety profile.

Specific Populations

Pregnancy

Cromolyn Sodium is classified as Pregnancy Category B. Animal studies have not shown harm to the fetus, but there aren't adequate studies in pregnant humans. If you're pregnant or planning to become pregnant, talk to your doctor about whether the benefits outweigh the risks.

Children

The oral solution is approved for children aged 2 and older. Dosing is typically adjusted by weight. The nasal spray (NasalCrom) is also approved for ages 2 and up. Cromolyn is generally well-tolerated in pediatric patients.

Kidney or Liver Problems

While Cromolyn has very low systemic absorption, small amounts are excreted by the kidneys. If you have kidney or liver impairment, your doctor may adjust your dose or monitor you more closely.

Older Adults

There are no specific dose adjustments recommended for older adults, but as with any medication, it's important to report any new or unusual symptoms to your doctor.

How to Manage Side Effects

If you're experiencing mild side effects, here are some strategies that may help:

• For nausea or stomach upset: Make sure you're taking Cromolyn on an empty stomach, 30 minutes before meals, as directed. Taking it with food can worsen GI symptoms. Also, don't mix the oral solution with fruit juice, milk, or food — use water only.
• For headache: Over-the-counter pain relievers like Acetaminophen (Tylenol) are generally safe to take with Cromolyn. Check with your doctor if headaches persist.
• For unpleasant taste: After drinking the solution, follow it with a sip of plain water. Some patients find that chilling the water helps.
• For diarrhea: Stay hydrated and eat bland foods. If diarrhea is severe or doesn't improve after a few days, contact your doctor. Keep in mind that diarrhea can also be a symptom of the underlying mast cell disorder.
• For skin rash or itching: Mild rashes may resolve on their own. If a rash spreads or is accompanied by other symptoms, call your doctor.

When to Call Your Doctor

Call your doctor if:

• Side effects are severe or don't improve after 1–2 weeks
• You experience signs of an allergic reaction (hives, swelling, trouble breathing)
• Your original symptoms get worse instead of better
• You develop new symptoms that concern you

Go to the emergency room if you have difficulty breathing, severe swelling, or signs of anaphylaxis.

What About Drug Interactions?

One of the advantages of Cromolyn is that it has very few drug interactions. Because it's barely absorbed into the bloodstream and isn't processed by the liver's cytochrome P450 enzymes, it doesn't interfere with most other medications. That said, always tell your doctor about everything you're taking, including supplements and OTC medications.

Final Thoughts

Cromolyn Sodium has one of the best safety profiles of any medication used for mast cell disorders. Most side effects are mild, temporary, and manageable. Serious reactions are rare.

If you've been prescribed Cromolyn and are having trouble finding it at your pharmacy, you're not alone — there's been an ongoing shortage since 2023. Use Medfinder to check which pharmacies near you have it in stock.