Which of the following drugs is used to treat attention deficit hyperactivity disorder (ADHD) and narcolepsy?

Methylphenidate is a central nervous system stimulant that is widely recognized for its efficacy in treating both attention deficit hyperactivity disorder (ADHD) and narcolepsy. As a stimulant, it works by increasing the levels of certain neurotransmitters, notably dopamine and norepinephrine, in the brain. This action helps enhance focus, attention, and impulse control, which are often impaired in individuals with ADHD.

In the case of narcolepsy, methylphenidate helps mitigate excessive daytime sleepiness by promoting wakefulness. Its dual indications make it a versatile medication in managing these conditions, as it effectively addresses the symptoms that characterize both ADHD and narcolepsy.

The other options have different therapeutic uses or mechanisms. Adderall, while it is also used to treat ADHD and narcolepsy, is composed of mixed amphetamine salts and operates similarly but is distinct from methylphenidate. Atomoxetine is a selective norepinephrine reuptake inhibitor specifically indicated for ADHD and does not have efficacy for narcolepsy. Modafinil is primarily used for narcolepsy and other sleep disorders but is not indicated for ADHD. Therefore, methylphenidate stands out for its approved use in both conditions.