Gut Feeling: How Fennel Cures Cramps and Digestive Discomfort

Foeniculum vulgare

Feb 27, 2025

Ancient Use

Fennel is one of the oldest medicinal herbs in the world. As early as 3000 BC, the Mesopotamians used it for its healing properties. Ancient Egyptians, Romans, Indians, and Chinese also incorporated fennel into their medicinal practices. In Greek mythology, Prometheus used a giant fennel stalk to steal fire from the gods and bring it to humanity. The Romans valued fennel for its ability to aid digestion and manage obesity, as well as to relieve cramping and flatulence. In this article, we will explore fennel’s role in alleviating gastrointestinal and menstrual discomfort.

Relevant Pathophysiology

Major sources of abdominal cramping pain are gastrointestinal disorders, such as irritable bowel syndrome (IBS) and dyspepsia (indigestion), and menstrual discomfort caused by uterine contractions.

IBS

In IBS, patients may experience abnormal spasms and contractions of the colon muscles, leading to pain, cramping, bloating, and irregular bowel movements. These disruptions can cause significant discomfort and irregular movement of food through the digestive tract. While the exact causes of IBS are still being studied, they appear to involve multiple factors, including hormonal imbalances, structural changes in the brain, increased nerve sensitivity in the digestive tract, mood disorders such as anxiety and depression, and alterations in the gut microbiome (1).

Dyspepsia

Dyspepsia, commonly known as indigestion, is described as episodic or persistent upper abdominal pain with many symptoms that can include abdominal pain/discomfort, heartburn, anorexia, nausea and vomiting, belching, and bloating. The causes of chronic indigestion are also still being elucidated, but can include impaired accommodation of the stomach, delayed gastric emptying, hypersensitivity of gastric neurons, and inflammation (2).

Dysmenorrhea

Dysmenorrhea, or pain during the menstrual cycle, is another common source of cramping abdominal pain. The pathophysiology is also not fully understood, but it is likely related to hypersecretion of prostaglandins from the uterus. Hormonal changes lead to increased prostaglandins which result in increased uterine contractions and pressure (3). This is why popular NSAID (Non-Steroidal Anti-Inflammatory Drug) medications like Midol and Ibuprofen can help relieve menstrual cramps by blocking the production of prostaglandins. Impaired uterine perfusion, ischemia, and sensitization of nerves likely also play a role.

Phytochemicals

Two major phytochemicals in fennel, anethole and estragole, are aromatic phenylpropanoids responsible for its characteristic odor and flavor.

Both compounds have been shown to reduce spasms in smooth muscles. Anethole modulates voltage-dependent calcium channels, which directly regulate muscle contraction (4). Studies indicate that estragole inhibits sodium channel activation (5), which could potentially reduce the heightened nerve sensitivity associated with IBS.

Animal studies suggest that anethole can restore delayed gastric emptying and stimulate gastric accommodation (6)—two key factors in indigestion. Additionally, anethole has been shown to lower prostaglandin E2 levels, the primary contributor to menstrual pain (7).

Anethole may also benefit the gut microbiome. Animal studies indicate that it improves intestinal barrier function, reduces inflammation, inhibits enterotoxigenic E. coli, and promotes the growth of beneficial gut bacteria (8).

Overall, anethole and estragole appear to influence sodium and calcium channels that regulate muscle contraction and nerve excitability, improve gastric motility, reduce prostaglandins, and enhance gut health—mechanisms that likely contribute to their effects on both gastric and menstrual pain.

Studies with Fennel and Gastrointestinal Symptoms

Below are several studies and their key findings demonstrating fennel’s ability to improve symptoms associated with various gastrointestinal issues:

IBS Study

The IBS study mentioned above, which investigated a combination of turmeric and fennel, was a placebo-controlled trial involving 121 patients. The researchers then conducted a larger study with 211 IBS patients, using bio-optimized extracts of turmeric and fennel oil across all IBS subtypes: diarrhea-predominant (IBS-D), constipation-predominant (IBS-C), and mixed (IBS-M) (10). Over two months, symptom severity improved across all subtypes, as shown in the graph below. Additionally, quality of life—including mental health, relationships, physical and social functioning, mood, and pain—showed improvement in all groups.

Studies on Fennel and Menstrual Symptoms

A meta-analysis of 12 studies (7 comparing fennel to NSAIDs and 5 comparing fennel to a placebo) involving over 500 females found that fennel was as effective as NSAIDs in alleviating pain from primary dysmenorrhea (18).

One placebo-controlled trial tested a 30 mg fennel extract capsule taken four times a day for three days from the start of the menstrual cycle. The results showed statistically significant improvements in pain intensity for all five hours after treatment and across all three days. Results from the study are shown below (19).

In another study involving 120 high school girls with dysmenorrhea, participants were randomized to receive either fennel extract or mefenamic acid, a potent NSAID (20). Mefenamic acid inhibits prostaglandin production, similar to ibuprofen and Midol. The study found that 80% of participants in the fennel group experienced improved or resolved pain, compared to 73% in the NSAID group. The full results are detailed in the table below.

An animal study confirmed that fennel essential oil exhibits strong anti-prostaglandin E2 activity by reducing the frequency of uterine contractions induced by prostaglandin E2 (21). This provides biochemical evidence for why fennel oil produces similar results to NSAIDs in clinical trials. For those looking to avoid chronic NSAID use due to risks such as renal toxicity, bleeding, or gastric ulcers, fennel may offer a safer alternative.

Fennel Toxicity: Is it Safe?

Fennel has been safely used for thousands of years. However, potential toxicity concerns exist with estragole. NIH toxicity studies found that extremely high doses (600 mg/kg) led to liver cancer in rats (22, 23). This dosage is drastically higher than the estimated 0.07 mg/day of estragole that an average adult consumes from dietary sources. A gram of fennel seeds contains approximately 0.1 to 14 mg of estragole (24).

Interestingly, the same studies showed that in rats with partial liver removal, estragole actually promoted liver regeneration. Additionally, fennel has been traditionally used to relieve infantile colic and support lactation in breastfeeding women. Given its long history of use, it is unlikely to be harmful in typical dietary amounts. However, concentrated forms should be used with caution due to this theoretical risk. For a detailed safety analysis of fennel in nursing mothers and infants, refer to this source (25).

Another potential side effect of fennel is nausea and vomiting, as it can alter gastrointestinal motility. It is advisable to start with a low dose and gradually increase/add other herbs as tolerated.

Personal Experience and Recommendations

During the peak of the pandemic, hospitalists at my hospital were required to wear N-95 masks throughout our nine-hour ER shifts. By the fifth hour, I would feel hungry and need to eat, which created the unpleasant issue of re-inhaling the scent of my food for the rest of my shift.

I had read about ancient yogis drinking CCF (cumin, coriander, fennel) tea to curb their appetite and settle their stomachs for prolonged meditation sessions. Curious, I started drinking CCF tea at the beginning of my shifts and found it effectively suppressed my appetite, allowing me to go 7-9 hours without hunger.

This highlights another important point—many traditional herbal remedies for gastrointestinal disorders combine multiple herbs rather than using fennel alone. For those exploring natural treatments for abdominal discomfort, experimenting with different combinations of cumin, coriander, fennel, anise, and ajwain may be beneficial.

Fennel can be consumed in capsule form, as fennel extract drops, or as tea. For abdominal cramping, I recommend trying it as a warm tea, which may enhance its soothing effects. A good starting dose is ½ teaspoon of fennel seeds in warm water, which can be increased if well tolerated. I have included the recipe I use for CCF tea below.

CCF Tea Recipe

Ingredients:

5 cups of water
1 teaspoon cumin seeds
1 teaspoon coriander seeds
1 teaspoon fennel seeds

Instructions:

Add water and seeds to a small pot and stir.
Bring to a boil, then simmer for 5 minutes.
Remove from heat and strain the seeds.
Pour into a mug and enjoy.

Acknowledgment

Special thanks to Dr. Malcolm Irani, MD, for sharing his valuable insights from a gastroenterologist’s perspective.

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