Somnolence is a common side effect of
antipsychotics. To assess the incidence of this side effect, we performed a MEDLINE search for randomized, double-blinded, placebo- or active-controlled studies of adult patients treated with
antipsychotics for
schizophrenia,
mania,
bipolar depression, or
bipolar disorder. We extracted rates of
somnolence from original publications and pooled them based on the dose of each
antipsychotic in the same psychiatric condition, then estimated the absolute risk increase (ARI) and the number needed to harm (NNH) of an
antipsychotic relative to placebo or an active comparator in the same psychiatric condition. According to the ARI in acute
schizophrenia, bipolar
mania, and
bipolar depression,
antipsychotics can be classified as high
somnolence (
clozapine), moderate
somnolence (
olanzapine,
perphenazine,
quetiapine,
risperidone,
ziprasidone), and low
somnolence (
aripiprazole,
asenapine,
haloperidol,
lurasidone,
paliperidone,
cariprazine). The risk of
somnolence with
blonanserin,
brexpiprazole,
chlorpromazine,
iloperidone,
sertindole, and
zotepine needs further investigation. The rates of
somnolence were positively correlated to dose and duration for some
antipsychotics, but not for others. Many factors, including
antipsychotic per se, the method used to measure
somnolence, patient population, study design, and dosing schedule, might affect the incidence of
antipsychotic-induced
somnolence. The mechanisms of
antipsychotic-induced
somnolence are likely multifactorial, although the blockade of
histamine 1 receptors and α1 receptors may play a major role. The management of
antipsychotic-induced
somnolence should include sleep hygiene education, choosing an
antipsychotic with a lower risk for
somnolence, starting at a lower dose with a slower titration based on psychiatric diagnoses, adjusting doses when necessary, and minimizing concurrent
somnolence-prone agents. Since most cases of
somnolence were mild to moderate, allowing tolerance to develop over at least 4 weeks is reasonable before discontinuing an
antipsychotic.