Benzodiazepines like clonazepam commonly cause drowsiness, ataxia, dysarthria, and nystagmus. Overdose with clonazepam is generally not life-threatening if the drug is taken alone, but may lead to areflexia, apnea, hypotension, cardiorespiratory depression, and coma. Coma, if it does occur, usually lasts a few hours but it can become more protracted and cyclical, especially in elderly patients. Increased frequency of seizures may occur in patients at supratherapeutic plasma concentrations. Benzodiazepine respiratory depressant effects are more serious when compounded in patients with respiratory disease.

An increased risk of congenital malformations associated with the use of benzodiazepine drugs like clonazepam has been suggested in several studies FDA Label F3763, F3796. There may also be non-teratogenic risks associated with the use of benzodiazepines during pregnancy FDA Label F3763, F3796. There have been reports of neonatal flaccidity, respiratory and feeding difficulties, and hypothermia in children born to mothers who have been receiving benzodiazepines late in pregnancy FDA Label F3763, F3796. In addition, children born to mothers receiving benzodiazepines late in pregnancy may be at some risk of experiencing withdrawal symptoms during the postnatal period FDA Label F3763, F3796. In general, it is best for patients who are of childbearing potential and also use benzodiazepines like clonazepam to discuss such matters with their health care professionals as careful consideration must be undertaken regarding the intersection of the risks of untreated seizure potential in the patient and any possible toxicity to the fetus FDA Label F3763, F3796.

Although the active ingredient of clonazepam has been found to pass into the maternal milk in small amounts only, mothers receiving clonazepam should not breast-feed their infants FDA Label F3763, F3796.

Since the possibility that adverse effects on the physical or mental development of the child could become apparent only after a number of years, the risk-benefit consideration of the long-term use of clonazepam in pediatric patients younger than five years of age is important FDA Label F3763, F3796.

The pharmacological effects of benzodiazepines like clonazepam appear to be greater in elderly patients than in younger patients even at similar plasma benzodiazepine concentrations, possibly because of age-related changes in drug-receptor interactions, post-receptor mechanisms, and organ function FDA Label F3763, F3796. In general elderly patients should be started on the lowest possible dose of clonazepam and observed closely FDA Label F3763, F3796. There is an increased risk for falls and fractures among elderly and debilitated benzodiazepine users FDA Label F3763, F3796. The risk is increased in those taking concomitant sedatives, including substances like benzodiazepines, alcoholic beverages, and so on FDA Label F3763, F3796.

Some oral LD50 values documented are >4000 mg/kg for the mouse model, >4000 mg/kg for the adult rat model, and >2000 mg/kg for the rabbit model ^F3763.