Methylphenidate, sold under the brand names Ritalin (/ˈrɪtəlɪn/ RIT-ə-lin) and Concerta (/kənˈsɜːrtə/ kən-SUR-tə) among others, is a central nervous system (CNS) stimulant used medically to treat attention deficit hyperactivity disorder (ADHD) and, to a lesser extent, narcolepsy.

Common adverse reactions of methylphenidate include: euphoria, dilated pupils, tachycardia, palpitations, headache, insomnia, anxiety, hyperhidrosis, weight loss, decreased appetite, dry mouth, nausea, and abdominal pain.[8] Withdrawal symptoms may include: chills, depression, drowsiness, dysphoria, exhaustion, headache, irritability, lethargy, nightmares, restlessness, suicidal thoughts, and weakness.

https://en.wikipedia.org/wiki/Methylphenidate