Polyphagia (extreme hunger) is a relatively uncommon symptom. It’s most often associated with undiagnosed or undertreated diabetes. Other causes include: Other hormone-related conditions. Mental health conditions. Rare medical conditions. Malnutrition in the form of undernutrition can also cause polyphagia. Undernutrition is a deficiency of nutrients. You may be undernourished if you don’t have an adequate diet, or if your body has trouble absorbing enough nutrients from your food. Certain medications, such as corticosteroids and cannabinoids (cannabis-related drugs), can cause polyphagia, as well. Talk to your healthcare provider if you experience extreme hunger after starting a new medication.