From Wikpedia:
Marjoram has long been used as a medicinal herb. Marjoram or marjoram oil has been used to treat cancer, colds, coughs, cramps, depression, as a diuretic, ear infections, gastrointestinal problems, headaches, and paralysis, as well as arthritis, chest congestion, and muscle aches. It has also been used as an aphrodisiac, mouthwash, tea, and in poultices, tinctures, and infusions. Though not all of its historic uses are scientifically backed, the plant has verifiable medical use. For example, it contains the phenol carvacrol, which is antibacterial, antifungal and antimicrobial. Ethanol extract is cytotoxic against fibrosarcoma cell lines, ethyl acetate extract has antiproliferative properties against C6 and HeLa cells, as have hesperetin and hydroquinone, which can be isolated from marjoram extract. Cardioprotective, hepatoprotective, antiulcerogenetic, anticholinesterase, anti-PCOS, and anti-inflammatory effects were also found in dried marjoram, marjoram tea, or in compounds extracted from marjoram.