Mdet SR 20 Tablet 15's is used to improve wakefulness in adult patients with attention deficit hyperactivity disorder (ADHD) (overactive and short attention span) and narcolepsy (excessive and uncontrollable daytime sleepiness). It contains Methylphenidate, which works by enhancing the amount of a chemical messenger known as dopamine in the brain, which controls our body's sleep-wake cycle. It reduces the reuptake of dopamine into nerves. In some cases, it may cause certain common side effects such as headache, fast heartbeat, diarrhoea, back pain, feeling anxious, nausea, trouble sleeping, feeling nervous, dizziness, stuffy nose, and upset stomach. Before taking this medicine, you should tell your doctor if you are allergic to any of its components or if you are pregnant/breastfeeding, and about all the medications you are taking and pre-existing medical conditions.