Which of the following medications is known as an anticonvulsant?

Valproic acid is an anticonvulsant medication primarily used to treat seizure disorders, including epilepsy, as well as bipolar disorder and to prevent migraine headaches. It works by increasing the availability of gamma-aminobutyric acid (GABA) in the brain, which is a neurotransmitter that has inhibitory effects on neuronal firing. This mechanism helps stabilize electrical activity in the brain and can effectively reduce the frequency and intensity of seizures in individuals with epilepsy.

In contrast, the other medications listed have different primary uses. Lithium is mainly used for mood stabilization in bipolar disorder, fluoxetine is an antidepressant that belongs to the selective serotonin reuptake inhibitors (SSRIs) class, and alprazolam is a benzodiazepine often prescribed for anxiety disorders and panic attacks rather than for seizure control. Therefore, valproic acid stands out as the correct choice due to its specific indication and mechanism of action in managing convulsive disorders.