The worst side effects of Lunesta (eszopiclone) include complex sleep behaviors like sleepwalking and sleep-driving, hallucinations, suicidal thoughts, and severe allergic reactions involving throat swelling. These are rare but serious enough that the FDA added its strongest safety warning, a black box warning, to the drug’s label. Most people taking Lunesta experience milder but still bothersome effects, with an unpleasant metallic or bitter taste being the single most common complaint, affecting up to 34% of users at the higher dose.
Complex Sleep Behaviors
The most dangerous side effects of Lunesta involve doing things while not fully awake. People have reported sleepwalking, cooking, eating, making phone calls, having sex, and even driving with no memory of it afterward. The FDA flagged these behaviors in a black box warning, noting they have led to serious injuries and deaths. These complex sleep behaviors appear to be more common with Lunesta and similar sleep medications (like zolpidem) than with other types of prescription sleep aids.
What makes these episodes especially dangerous is that you won’t know they’re happening. You may only find out the next morning from evidence you left behind or from someone else in the household. If this happens even once, the medication should be stopped.
Hallucinations and Psychiatric Effects
In clinical trials, about 2.4% of people taking Lunesta experienced hallucinations, compared to 0% on placebo. These could be visual or auditory, and they were significant enough that six participants had to stop the medication because of them. At the 3 mg dose specifically, 3% of trial participants reported hallucinations.
Other psychiatric effects showed up in trials at lower rates but are still worth knowing about. Suicidal thoughts occurred in 0.7% of people taking Lunesta in phase 3 studies, with no cases in the placebo group. Worsening depression appeared in 0.3% of users. Confusion affected 3% of people on the 3 mg dose. Anxiety, nervousness, and decreased sex drive also appeared more frequently in people taking the drug than in those taking a placebo.
The Metallic Taste Problem
Lunesta is notorious for causing a bitter or metallic taste that lingers, often into the next day. This isn’t just a minor annoyance for many users. In clinical trials, 34% of people on the 3 mg dose reported an unpleasant taste, compared to just 3% on placebo. At the 2 mg dose, 17% reported it. A more detailed study found the real number may be even higher: when researchers specifically asked about taste changes, 62% of participants reported bitter or metallic sensations during treatment.
There’s no well-established way to get rid of this taste. It tends to persist as long as you’re taking the medication, and for many people it’s the reason they stop.
Next-Day Drowsiness and Dizziness
Daytime sleepiness affected 8 to 10% of Lunesta users in trials, roughly three times the rate seen with placebo. Dizziness hit 5 to 7% of users depending on the dose. For older adults, dizziness was reported by 6% at the 2 mg dose, and accidental injuries were three times more common than with placebo, likely related to unsteadiness and sedation.
Interestingly, one driving study found no measurable difference in brake reaction time, cognitive function, or psychomotor performance the morning after a 3 mg dose compared to placebo. That said, individual responses vary, and the clinical trial data clearly shows a meaningful percentage of people do feel impaired the next day.
Severe Allergic Reactions
Lunesta can trigger anaphylaxis or angioedema, a rapid swelling of the face, lips, tongue, or throat. This is rare but potentially life-threatening if the swelling restricts your airway. Skin rash occurred in 3 to 4% of users in trials. If you notice swelling in your face or throat, difficulty breathing, or sudden weakness after taking Lunesta, that’s a medical emergency.
Withdrawal and Rebound Insomnia
Stopping Lunesta after regular use can cause withdrawal symptoms including anxiety, sweating, irritability, muscle spasms, tremors, nausea, poor concentration, and mood swings. The most common rebound effect is insomnia that’s actually worse than what you had before starting the medication, often accompanied by intense anxiety that can escalate to panic attacks. The good news is that rebound insomnia and anxiety typically peak and resolve within a few days, though the experience can be rough.
Tapering off gradually rather than stopping abruptly reduces the severity of these withdrawal effects.
Risks With Alcohol and Other Sedatives
Combining Lunesta with alcohol amplifies its sedating effects, increasing dizziness, drowsiness, and impaired judgment beyond what either substance causes alone. The same applies to opioids, benzodiazepines, and other drugs that depress the central nervous system. This combination raises the risk of dangerously slowed breathing, excessive sedation, and the complex sleep behaviors described above. Alcohol should be completely avoided while taking Lunesta.
Common Side Effects by the Numbers
Beyond the serious risks, the everyday side effects that show up most often in clinical trials paint a clear picture of what to expect:
- Unpleasant taste: 17 to 34% (dose-dependent)
- Headache: 17 to 21%
- Daytime sleepiness: 8 to 10%
- Dizziness: 5 to 7%
- Dry mouth: 5 to 7%
- Nausea: 4 to 5%
- Respiratory infection: 5 to 10%
Older adults experienced a somewhat different profile. Abnormal dreams, nerve pain, itching, and urinary tract infections appeared in their trials but weren’t prominent in younger adult studies. Accidental injuries were also a distinct concern in the elderly group, reported by 3% compared to 1% on placebo.
Most of these common side effects are dose-dependent, meaning they get worse at higher doses. The metallic taste is the clearest example, doubling from the 2 mg to the 3 mg dose. Starting at the lowest effective dose reduces the likelihood and intensity of most side effects.