Collagen is increasingly used as a supplement to support tendon health and potentially treat tendonitis, based on emerging scientific evidence rather than long-standing tradition. Tendons are primarily composed of type I collagen, and tendon injuries such as tendonitis involve degeneration or microtears in the collagen matrix. The rationale behind collagen supplementation is that providing the body with collagen peptides may supply the necessary building blocks (amino acids) for tendon repair and regeneration.

Several small-scale studies and animal models suggest that oral hydrolyzed collagen can enhance tendon healing, improve collagen synthesis, and reduce markers of inflammation. Human clinical trials remain limited; however, a few randomized controlled trials have shown that supplementation with collagen peptides, especially when combined with physical therapy or exercise, may improve tendon function, reduce pain, and support recovery from tendon injuries. For example, a 2019 study published in Applied Physiology, Nutrition, and Metabolism reported improved Achilles tendon properties in individuals who consumed collagen supplements before exercise.

Despite these promising findings, the overall quality and quantity of evidence remain low. Most studies have small sample sizes, short durations, and potential conflicts of interest. There is not yet a strong consensus among clinicians, and collagen is not considered a standard treatment for tendonitis. Thus, the evidence supporting collagen's use for tendonitis is best described as preliminary, warranting further, larger-scale research.