What common side effect might a client receiving phenobarbital sodium experience?

Phenobarbital is a barbiturate used primarily as a sedative and anticonvulsant. One of the most common side effects associated with phenobarbital sodium is drowsiness. This sedative effect arises from its action on the central nervous system, where it enhances the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). The increased GABAergic activity leads to CNS depression, resulting in drowsiness and sedation, which can be particularly pronounced when treatment first begins or when dosage adjustments are made.

While other side effects, such as nausea, anxiety, and insomnia, may occur with phenobarbital use, drowsiness is the most notable and frequently reported side effect. Patients receiving this medication are often advised not to operate heavy machinery or perform tasks requiring full alertness until they understand how the drug affects them.