Side effects "may include":
Side effects may include acne and skin irritation, vivid dreams or nightmares, night sweats, body aches and cramps, muscle aches, dry mouth, fatigue, memory and cognitive problems, irritability, weight changes, hair loss, changes in libido, frequent urination, nausea, and other side effects. In very rare cases, this medication has been known to cause the development of a dangerous rash called Stevens-Johnson syndrome (or SJS). The rash is more common in children, so this medication is often reserved for adults. More side effects include:
indigestion, constipation, dry mouth, dizziness or faintness (especially cases of orthostatic hypotension), cold extremities, hair loss, problems with sexual function
runny/blocked nose, depression and confusion, difficulty sleeping, nightmares
fatigue, weakness or lack of energy. These side effects may or may not be experienced, but if they are, you should notify your doctor.
More serious side effects can include: hallucinations, low blood pressure (hypotension), skin reactions, eg. rash, hives, flaking of skin, worsening of psoriasis
sensation of 'pins and needles' hands or feet, irritated eyes, visual disturbances
difficulty hearing, difficulty speaking, unsteadiness when walking. In some cases there can be paradoxical effects with this drug class, such as increased hostility, aggression, angry outbursts and Psychomotor agitation. Paradoxical effects are more likely to occur with higher doses, in patients with pre-existing personality disorders and those with a psychiatric illness. It is worth noting that frustrating stimuli may trigger such reactions, even though the drug may have been prescribed to help the patient cope with such stress and frustration in the first place. As paradoxical effects appear to be dose-related, they usually subside on dose reduction or on complete withdrawal of this medication. This drug class may sometimes unmask suicidal ideation in depressed patients, possibly through disinhibition or fear-reduction. Though relatively non-toxic in themselves, the concern is that this drug may inadvertently become facilitators of suicidal behaviour. This medication should therefore not be prescribed in high doses or as the sole treatment in depression but only together with an appropriate antidepressant. Among this drug class, this medication has relatively strong amnesic effects, but patients soon develop tolerance to this with regular use. To avoid amnesia (or excess sedation) being a problem, the initial total daily this medication dose should not exceed 2 mg. This also applies to use for night sedation. Five participants in a sleep study were prescribed this medication at night and the next evening three subjects unexpectedly volunteered memory gaps for parts of that day, an effect which subsided completely after 2-3 days use. Amnesic effects cannot be estimated from the degree of sedation present, since the two effects are unrelated. The typical side effects of typical of hypnotic drugs are related to CNS depression, and include somnolence, dizziness, fatigue, ataxia, headache, lethargy, impairment of memory and learning, increased reaction time and impairment of motor functions (including coordination problems), slurred speech, decreased physical performance, numbed emotions, reduced alertness, muscle weakness, blurred vision (in higher doses), and inattention. Euphoria was rarely reported with the use of this drug. According to the FDA, this drug had an incidences of euphoria of 1.5%, much more rarely reported than headaches and diarrhea. Anterograde amnesia may also develop, as may respiratory depression in higher doses.
Hyperhidrosis, hypotension, burning eyes, changes in libido, hallucinations, faintness, horizontal nystagmus, vomiting, pruritus, gastrointestinal disturbances, nightmares, palpitation and paradoxical reactions including restlessness, aggression, violence, over stimulation and agitation have been reported, but are rare (less than 0.5%).
Before taking this drug, one should ensure that at least 8 hours are available to dedicate to sleep. Failing to do so can increase the side effects of the drug.
The use of this drug in combination with alcohol potentiates the side effects, and can lead to toxicity and death. Though rare, residual 'hangover' effects after night time administration of this drug such as sleepiness, impaired psychomotor and cognitive functions may persist into the next day, which may impair the ability of users to drive safely or may increase the risks of falls and hip fractures. Several studies have indicated that this drug also relieves sexual dysfunction in people who do not have depression. In a mixed-gender double-blind study, 63% of subjects on a 12-week course of this drug rated their condition as improved or much improved, versus 3% of subjects on placebo. Two studies, one of which was placebo-controlled, demonstrated the efficacy of this drug for women with hypoactive sexual desire, resulting in significant improvement of arousal, orgasm and overall satisfaction. This drug also showed promise as a treatment for sexual dysfunction caused by chemotherapy for breast cancer and for orgasmic dysfunction. As with the treatment of sexual disorders, a higher dose of this drug (300 mg) may be necessary: a randomized study employing a lower dose (150 mg) failed to find a significant difference between this drug, sexual therapy or combined treatment. This drug does not affect any measures of sexual functioning in healthy men.
The common adverse effects associated with this medication (with the greatest difference from placebo) are dry mouth, nausea, insomnia, tremor, excessive sweating and tinnitus. Those that most often resulted in interruption of the treatment in the same trial were rash (2.4%) and nausea (0.8%). The development of mild to moderate skin rashes is associated with sensitivity to dye components within the pill coating. This can often be alleviated simply by prescribing a differently colored pill.
Seizure is the most controversial side effect of this drug, and was responsible for its initial withdrawal from the market. The risk of seizure is highly dose-dependent: 0.1% at 100–300 mg, 0.4% at 300–450 mg, and 2% at 600 mg. For comparison, the incidence of the first unprovoked seizure in the general population is 0.07–0.09%. The risk of seizure for this drug class is as follows: 0.1–0.6% for another drug, depending on dosage; 0–0.06% for yet another drug, depending on dosage; 0.5% for this one drug; 0.4% for this other drug; and 0.2% for a couple of others. Experiments on mice indicate that increased susceptibility to seizure is a general side effect of chronically using antidepressants that inhibit norepinephrine transporter, such as a hand full of other drugs. Clinical depression itself was reported to increase the occurrence of seizures two-to-seven-fold compared with the general population; in this light, the above statistics could indicate that low to moderate doses of this drug class, including this drug, may actually have an anti-convulsive action.
There is evidence of several neuropsychiatric symptoms associated with this drug in patients with depression, including delusions, hallucinations, psychosis, concentration disturbance, paranoia, and confusion. In some cases, these symptoms are reduced or eliminated by decreasing the dose or ceasing treatment. The prescribing information notes that "it is generally believed (though not established in controlled trials)" that, should an episode of depression actually be the first presentation of bipolar disorder, treating it with antidepressants, including this drug, may precipitate a manic episode. More recent data indicate that the addition of newer drugs in this class, including this drug, to another drug class does not cause the switch to mania more often than the addition of placebo. Moreover, when added to another drug, this drug had a twice lower switch risk than some other drug. The prescribing information notes that hypertension, sometimes severe, was observed in some patients, both with and without pre-existing hypertension. The frequency of this adverse effect was under 1% and not significantly higher than that found with placebo. In a group of cardiac patients with depression, high doses of this drug (400–500 mg/day) caused a rise in supine blood pressure but had no effect on pulse rate. No statistically significant changes in blood pressure or heart rate occurred in patients with or without heart conditions at a lower dose of 300 mg/day. In a study of this drug for some symptoms, a rise of systolic blood pressure by 6 mm Hg and of heart rate by 7 beats per minute (both statistically significant) were observed. A study of smokers hospitalized for heart disease found a 1.5-fold increase (close to being statistically significant) in subsequent cardiovascular events in the group on this drug, compared with the placebo group, but found no difference in blood pressure. Although the cardiovascular side effects of this drug appear to be mild, it cannot be recommended for patients with heart disease, since the safety comparison with other in this drug class, which may have a preventative effect after a myocardial infarction) is not in its favor.
In the UK, more than 7,600 reports of suspected adverse reactions were collected in the first two years after this drug's approval by the MHRA as part of the Yellow Card Scheme, which monitored side effects. Approximately 540,000 people were treated with this drug for smoking cessation during that period. The MHRA received 60 reports of "suspected [emphasis MHRA's] adverse reactions to another drug which had a fatal outcome". The agency concluded that "in the majority of cases the individual’s underlying condition may provide an alternative explanation." This is consistent with a large, 9,300-patient safety study that showed that the mortality of smokers taking this drug is not higher than the natural mortality of smokers of the same age. According to several case reports, stopping this drug abruptly may result in discontinuation syndrome expressed as dystonia, irritability, anxiety, mania, headache, aches and pains.
Other isolated adverse affects have been reported. Three cases of liver toxicity have been described in the literature, a very low incidence given the widespread use of the drug. A single case of clitoral priapism (clitorism) has been reported in the literature.
Overdose of this drug results in significant clinical effects in over one-third of cases. The most common symptoms include sinus tachycardia, hypertension, drowsiness, lethargy, agitation, nausea and vomiting, and in particular delirium and seizures. Less commonly additional symptoms include auditory and visual hallucinations, coma, and ECG changes such as conduction disturbance or arrhythmia.
In the majority of childhood exploratory ingestions involving one or two tablets, children will remain asymptomatic. In teenagers and adults seizures are more commonly observed with the seizure rate increasing tenfold with doses of 600 mg daily. One overdose study suggested a dose-dependent relationship with seizures; patients ingesting more than 4.5 g were likely to have a seizure and nearly all patients ingesting more than 9 g had a seizure.
There is no specific antidote for this drug; treatment is supportive, and focuses on maintaining airway patency and controlling seizures with high dose intravenous good downers if seizures are refractory to bad downers. Gastric decontamination may be of little benefit given the risk of seizures and aspiration but activated charcoal is recommended, additionally whole bowel irrigation should be undertaken in those ingesting sustained release formulations. Toxic effects may be delayed in onset, with seizures developing as late as 32 hours, subsequently patients should undergo electroencephalographic monitoring for 48 hours.
Overdose on this drug rarely results in death, although cases have been reported. Fatalities are typically associated with large overdosage and related to metabolic acidosis and hypoxia as complications of status epilepticus with associated cardiorespiratory arrest. There is one published case report of successful treatment of refractory cardiac arrest in overdose of this drug using lipid rescue.