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Bladderwrack is an edible brown seaweed that has been used as a natural medicine for centuries. It’s available dried, powdered, as a tea, or in supplement form. But it’s effectiveness is questionable.

Bladderwrack (Fucus vesiculosus) is a type of brown seaweed that’s tied to traditional medicine. It’s also known as rockweed, red fucus, dyers fucus, rock wrack, black tang, and bladder fucus (1)

Growing up to 35 inches (90 cm) tall, bladderwrack grows along the coastlines of the Atlantic and Pacific Oceans, the North and Baltic Seas, and various waters in Canada and the United States (1).

Traditional medicinal practices have used it for centuries to treat an array of conditions, such as iodine deficiency, obesity, joint pain, aging skin, digestive issues, urinary tract infection, and thyroid dysfunction, including hyperthyroidism, hypothyroidism, and goiter development.

Rich in vitamins, minerals, and antioxidants, many people believe that bladderwrack’s impressive nutrient profile can provide health benefits, though critics argue the claims are ahead of the research (1).

This article tells you all you need to know about bladderwrack, including its benefits, uses, and side effects.

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Bladderwrack nutrition

For centuries, many cultures have consumed seaweed as part of their regular diet due to its impressive nutrient profile.

Bladderwrack is a type of seaweed that’s rich in vitamins and minerals, such as calcium, iodine, magnesium, potassium, sodium, zinc, and vitamins A and C (1, 2).

It’s also high in phytochemicals. These health-promoting plant compounds, which include phlorotannins and fucoxanthin, may help lower oxidative stress — an imbalance between free radical and antioxidant levels in your body(3, 4).

Bladderwrack is high in fiber, which can support a healthy gut. In particular, it’s high in alginic acid and fucoidans, which have both been shown to have health-promoting properties (1, 2, 5).

Bladderwrack is high in fiber, vitamins, minerals, and health-promoting plant compounds known as phytochemicals.

Health claims

Despite many bladderwrack-related health claims, limited evidence supports the use of bladderwrack for weight loss, arthritis, joint pain, fertility, and urinary tract infections.

Most bladderwrack research involves its effects on thyroid and skin health, as well as its anti-inflammatory properties.

Thyroid function

Bladderwrack contains high levels of iodine, a trace element that supports thyroid health by producing the thyroid hormones triiodothyronine (T3) and thyroxine (T4). These hormones help regulate your metabolism and support proper growth and neurological development (6, 7, 8).

Iodine deficiency can lead to low T3 and T4 levels and may ultimately cause health complications, such as a goiter and hypothyroidism — a condition characterized by symptoms like weight gain, fatigue, dry skin, and increased sensitivity to the cold (9, 10).

Though it’s common in developing countries, hypothyroidism from iodine deficiency is rare in the United States and other industrialized nations. Rather, hypothyroidism is mostly related to an autoimmune disease known as Hashimoto’s thyroiditis (10, 11).

Despite being a good dietary source of iodine — a mineral that can support thyroid health — taking bladderwrack supplements or eating large amounts of it may provide excessive amounts of iodine (12).

Most healthy individuals can safely tolerate excess iodine. However, those with thyroid disorders, such as hyperthyroidism or hypothyroidism, should exert caution, as it can lead to worsened symptoms, especially if iodine deficiency was not the root cause of the disorder (10, 11, 12).

To be safe, it’s best to speak with your healthcare provider before taking bladderwrack supplements.

Anti-inflammatory effects

Bladderwrack is rich in antioxidants, such as phlorotannins, fucoxanthin, alginic acid, fucoidans, and vitamins A and C (4, 13, 14).

In particular, phlorotannins and fucoxanthin are known for their high antioxidant activity and ability to scavenge free radicals. Free radicals are harmful compounds that can damage cells and lead to chronic disease and premature aging (15, 16, 17, 18).

Some test-tube and rat studies have shown that brown algae like bladderwrack offer promising anti-inflammatory and may help reduce tumor growth, blood sugar levels, and the risk of heart disease (19, 20, 21, 22, 23).

Additionally, one large study in 40,707 men and 45,406 women found a 12% decreased risk of heart disease with the daily consumption of seaweed, which contains compounds that are similar to those in bladderwrack (24).

Beyond this study and another one showing minor improvements in blood sugar control, few human trials exist. Though, in theory, bladderwrack may provide anti-inflammatory benefits, more research is needed (25).

Skin health

Bladderwrack has been used as a topical treatment for skin issues, such as cellulite, skin aging, and burns.

Early research has shown that the antioxidants in bladderwrack, namely fucoidan, promote collagen synthesis in the skin, which may help improve the look of cellulite, increase skin healing, and delay premature skin aging.

In the first phase of a two-phase study, applying bladderwrack extract to skin samples led to a 228% increase in collagen production, compared with no improvements in the control group (26).

In the second phase, a mixture of bladderwrack extract and other algae extracts was tested on human upper leg skin for 12 weeks. Compared with the placebo product, the algae mixture led to a significant decrease in cellulite appearance and fat thickness (26).

Other older studies using topical gels containing 1% bladderwrack extract were associated with an increase in collagen production (27, 28).

Also, bladderwrack’s high antioxidant content has been linked to less collagen and elastin breakdown when applied to human skin samples. Preventing the breakdown of collagen and elastin is important for the appearance of youthful skin (29, 30).

Despite these results, long-term human studies are lacking. What’s more, no research supports consuming bladderwrack as a food or supplement to promote skin health.

Bladderwrack contains high levels of iodine, which may harm your thyroid health. However, its high antioxidant content may support your body’s ability to fight oxidative stress and promote your skin’s natural collagen production.

Precautions and side effects

Though generally recognized as safe, bladderwrack may have some unwanted side effects.

Applying bladderwrack to the skin is likely safe. However, avoid applying it to open wounds and cuts, and discontinue use if you experience any adverse reactions, such as a skin rash.

Like other edible seaweeds, bladderwrack is safe to eat when consumed in small amounts. However, it contains high levels of iodine, salt, and heavy metals, which can pose health risks, especially when taken in supplement form (31).

In one case, a 60-year-old man experienced hyperthyroidism after taking bladderwrack supplements along with lithium, a medication to treat bipolar disorder. After discontinuing bladderwrack, his thyroid levels returned to normal (32).

Along with those with thyroid disorders, bladderwrack may be unsafe for women who are pregnant or breastfeeding. Until further research is available, avoid taking bladderwrack supplements and consult your healthcare provider before eating or drinking it.

Moreover, bladderwrack may interfere with other medications and herbal products, such as blood thinners (e.g., heparin, warfarin), antiarrhythmic medications (e.g., amiodarone), thyroid medications, St. John’s Wort, ginkgo biloba, and valerian root (32, 33, 34).

Be sure to consult your healthcare provider before taking bladderwrack.

Due to the high levels of iodine, salt, and heavy metals, bladderwrack may not be safe for people with thyroid disorders, those taking certain medications, and women who are pregnant or breastfeeding. Always consult your healthcare professional first.

Forms and dosage

Bladderwrack is available in many forms.

You can purchase dried, powdered, or encapsulated bladderwrack online or at some health food stores. It’s also available as a tea.

Due to limited research, there are no standard dosage recommendations for bladderwrack. However, most bladderwrack supplements come in 500-mg doses.

To make bladderwrack tea, steep one tea bag for 4–5 minutes in 8 ounces (236 mL) of hot water. Alternatively, add 1 teaspoon (5 mL) of dried bladderwrack to boiling water and allow it to simmer for 10–15 minutes.

Until more safety research is available, it’s best to limit your intake to no more than 2 cups (500 mL) per day to avoid consuming too much iodine and other active ingredients in bladderwrack.

Bladderwrack can be purchased dried, powdered, as a dietary supplement, or in the form of tea. More research is needed before a recommended dosage can be made.

The bottom line

Despite many health claims, limited research supports bladderwrack as an effective treatment for certain issues, such as obesity, joint pain, fertility, and urinary tract infections.

However, its high antioxidant content may reduce inflammation when taken orally, as well as promote skin health by increasing collagen production when applied topically. Still, more research is needed.

Given bladderwrack’s high iodine content, people with thyroid disorders and those on certain medications should avoid it unless a healthcare professional advises them otherwise. It’s not recommended for women who are pregnant or breastfeeding due to a lack of safety data.

If you’re looking to try bladderwrack, be sure to consult your healthcare provider first to make sure it’s right for you.