Rockweed refers to several species of brown seaweed, particularly those in the genus Ascophyllum or Fucus, such as Ascophyllum nodosum and Fucus vesiculosus. These seaweeds have historically been used in various traditional medicine systems, particularly in Europe and along coastal regions, to support thyroid health. The primary rationale behind this traditional use is their naturally high iodine content. Iodine is an essential trace mineral required for the synthesis of thyroid hormones, and deficiency in iodine is a well-known cause of thyroid dysfunction, including goiter and hypothyroidism.

Traditional herbalists and folk medicine practitioners have recommended rockweed and other seaweeds as dietary sources of iodine, especially in areas where iodine deficiency was common due to low levels in soil and food. However, while the link between iodine and thyroid function is scientifically established, the use of rockweed specifically for thyroid health is mainly based on its iodine content and traditional use rather than on robust clinical trials. There is a lack of modern scientific studies that directly evaluate rockweed supplementation for thyroid conditions in humans. Additionally, excessive intake of iodine from seaweed can lead to thyroid dysfunction in susceptible individuals. Therefore, while the traditional use is supported, scientific evidence specific to rockweed is limited.