Phycocyanins are blue pigments derived mainly from cyanobacteria such as Spirulina. In recent years, there has been growing scientific interest in their potential neuroprotective properties, including relevance to Alzheimer's disease (AD). Several preclinical studies (in vitro and animal models) have shown that phycocyanins possess antioxidant, anti-inflammatory, and anti-apoptotic effects, which may theoretically help mitigate some pathways implicated in the progression of AD, such as oxidative stress and neuroinflammation. For example, some rodent studies suggest that phycocyanin administration can reduce amyloid-beta-induced neurotoxicity, improve oxidative stress markers, and enhance cognitive performance in AD models.

However, no well-designed human clinical trials have been published to date that demonstrate efficacy of phycocyanins in preventing or treating Alzheimer's disease in humans. Most available evidence is limited to laboratory and animal research, which cannot be directly extrapolated to clinical use in people with AD. Thus, while there is a scientific rationale and some promising preclinical findings, the overall evidence remains weak (rated 2/5) and insufficient for recommending phycocyanins as a treatment or supportive intervention for Alzheimer's disease at this time.