What is Zopiclone and How Does It Work?

Zopiclone is a widely prescribed sleeping tablet in the UK, used for the short-term treatment of insomnia. It belongs to a class of medicines called cyclopyrrolones — sometimes referred to as “Z-drugs” — and works by acting on the central nervous system to slow brain activity and encourage sleep.

It works by enhancing the effect of a neurotransmitter called GABA (gamma-aminobutyric acid), which is the brain’s primary inhibitory chemical. By boosting GABA activity, zopiclone produces a calming, sedative effect that helps you fall asleep faster, stay asleep longer, and reduces night-time waking.

Zopiclone is available in several dosage strengths, including 3.75mg, 7.5mg, 10mg, 20mg, and 25mg tablets, with 7.5mg being the most commonly prescribed dose for adults in the UK. It is typically taken once per night, just before bedtime.

Why Does Zopiclone Cause a Bitter Taste?

The bitter or metallic taste is one of the most well-documented and frequently reported side effects of zopiclone. It is so common that it is listed as a known side effect in the official UK patient information leaflet for the medicine. But what actually causes it?

There are two main reasons why zopiclone causes this unpleasant taste:

1. Zopiclone Is Secreted in Saliva

After zopiclone is absorbed into your bloodstream, it is metabolised by the liver. During this process, small amounts of zopiclone and its metabolites are excreted into your saliva through the salivary glands. This is the primary reason for the bitter taste.

The drug’s chemical compounds — particularly its cyclopyrrolone structure — are inherently bitter in taste. As saliva continuously circulates in your mouth throughout the night and into the next morning, these compounds keep reintroducing that distinctive bitterness. No amount of brushing your teeth immediately after waking will fully eliminate it, because the taste is being actively secreted from your body — not just sitting on your tongue from the tablet itself.

2. The Chemical Composition of Zopiclone Itself

Zopiclone belongs to a group of compounds that are chemically inherently bitter at a molecular level. Bitterness is detected by taste receptor cells (TRCs) on the tongue that respond to specific chemical structures. The cyclopyrrolone ring in zopiclone’s molecular structure triggers these bitter taste receptors (specifically the TAS2R family of receptors) even in trace amounts.

This means the bitter taste is a direct pharmacological property of the drug — it cannot be removed by changing the tablet coating or taking it with water. The taste arises from within, not from the pill itself.

The Science Behind the Metallic Taste

Many people describe the taste left by zopiclone not just as bitter but also as metallic — similar to sucking on a copper coin or eating a metallic-tasting food. This metallic quality has a slightly different explanation.

The metallic sensation occurs because zopiclone metabolites interact with specific taste receptor proteins in the mouth that detect both bitterness and metallic sensations. Some of these receptors overlap, which is why certain medicines produce both a bitter and metallic taste simultaneously.

Additionally, zopiclone can slightly reduce saliva production (a common anticholinergic-like effect seen in many sleep medicines), which can intensify the perceived bitterness — because less saliva means the bitter compounds become more concentrated in the mouth.

How Long Does the Bitter Taste Last?

The duration of the bitter taste depends on several factors, including your individual metabolism, the dose taken, and your hydration levels. Generally speaking:

For most people, the bitter taste is most intense in the first 1–3 hours after waking and gradually subsides throughout the morning. If you find the taste persists well into the afternoon or beyond, it may be worth speaking to your doctor, as this could indicate the drug is clearing your system more slowly than expected.

8 Practical Tips to Reduce the Bitter Taste from Zopiclone

While you cannot completely eliminate the bitter taste — as it is a pharmacological property of zopiclone — there are several practical strategies that many users find significantly reduce its intensity and duration.

Other Common Side Effects of Zopiclone

The bitter or metallic taste is the most widely reported side effect of zopiclone, but it is not the only one. Understanding the full range of potential side effects helps you use the medication safely and know when something needs medical attention.

When to Speak to Your Doctor

The bitter taste from zopiclone is unpleasant but generally harmless and temporary. However, there are certain situations where you should discuss your experience with a GP or pharmacist:

• The bitter taste is persisting well beyond 8–10 hours after waking and is significantly affecting your quality of life
• You are experiencing a persistent metallic taste even on days when you have not taken zopiclone — this could indicate another medical issue
• The taste is accompanied by nausea, difficulty eating, or significant dry mouth
• You notice signs of dependence — such as needing higher doses to sleep, or experiencing anxiety, sweating, or insomnia when you miss a dose
• You are taking zopiclone for longer than 4 weeks without a medical review

Does Eszopiclone Cause Less Bitter Taste?

Eszopiclone (sold under the brand name Lunesta in the US) is the active S-enantiomer of zopiclone — essentially a refined, single-isomer version of the same drug. It is available in the UK through licensed online pharmacies and specialist prescribers.

Unfortunately, eszopiclone is also associated with a bitter or metallic taste, and in clinical trials it was one of the most commonly reported side effects — affecting a significant proportion of users. Because it shares the same core cyclopyrrolone chemical structure as zopiclone, the same mechanism (salivary secretion of bitter compounds) applies.

Some users report that lower doses of eszopiclone (1mg or 2mg) produce a slightly less intense aftertaste compared to standard zopiclone 7.5mg — though clinical evidence for this is mixed. If you find zopiclone’s taste particularly distressing, it may be worth discussing eszopiclone as an alternative with your doctor.

Frequently Asked Questions

Conclusion

The bitter or metallic taste that zopiclone leaves behind is one of its most recognisable — and most complained about — side effects. It happens because zopiclone’s inherently bitter chemical compounds are secreted directly into your saliva as the drug is metabolised, and no amount of brushing will eliminate it completely until the drug clears your system.

While it cannot be entirely prevented, practical strategies — drinking water immediately on waking, brushing your teeth and tongue, chewing sugar-free mint gum, eating breakfast, and staying well hydrated — can meaningfully reduce both the intensity and the duration of the taste. If the bitterness is significantly affecting your day-to-day life, speak to your doctor about whether a lower dose or an alternative medication might be more appropriate for you.