Epilepsy can be controlled with medication in most cases, however, around 30% of adult patients remain pharmacoresistant. Ketogenic diet (KD) and its variants have been used as a therapy in children with epilepsy for over a hundred years and they have been proven to be an effective method of controlling refractory epilepsy. Adult patients could also benefit from this method of controlling seizures, however, the studies evaluating its efficacy are limited and the diet is not as widely used in this group of patients. The diet works by mimicking a fasting state in which ketone bodies become the primary source of energy. However, the exact mechanisms underlying the anticonvulsant effects of the diet are not yet fully understood. This review aims to assess the effectiveness of ketogenic diet and its subtypes in controlling drug-resistant epilepsy (DRE) in adults, discusses possible mechanisms of its anticonvulsant action, potential adverse effects, and applicability of this method in managing epilepsy. It also compares different variants of the diet and provides practical guidelines on introducing and maintaining the KD therapy.