Silymarin is a flavonolignan mixture found in Silybum (milk thistle) seeds; it exhibits antiviral, anti-inflammatory, anti-fibrotic, hepatoprotective, neuroprotective, immunosuppressive, antioxidative, and anticancer activities. Silymarin inhibits influenza virus proliferation by suppressing viral RNA synthesis. In animal models of benign prostatic hyperplasia (BPH), silymarin decreases inflammation, collagen deposition, and levels of iNOS, COX-2, NF-κB, IL-6, IL-8, and HIF-1α. In animal models of fibrosis, silymarin decreases oxidative stress, fibrosis development, and levels of α-SMA and TGF-β1. Silymarin shows potential benefit in models of Parkinson’s disease and Alzheimer’s disease, inhibiting aggregation of proteins such as amyloid-β (Aβ). In activated T cells, silymarin induces G1 phase cell cycle arrest and decreases mTOR signaling. This compound decreases lipid peroxidation and increases radical scavenging and levels of glutathione in vivo. In ovarian cancer cells, silymarin increases expression of PTEN, decreases signaling by Akt and expression of Bcl-2, induces apoptosis, and inhibits cellular proliferation; it also inhibits telomerase activity.