Melatonin is a hormone that helps regulate your sleep cycle, often used as a supplement for sleep issues or jet lag. In the UK, it’s a prescription-only medicine due to its potential to affect hormone levels and interact with other medications. While melatonin is generally safe, it can cause side effects, including:
- Mild effects: Drowsiness, grogginess, headaches, or stomach discomfort.
- Serious effects (rare): Blurred vision, dizziness, mood changes, or allergic reactions like swelling or difficulty breathing.
Factors like dosage, timing, age, health conditions, and interactions with medications can influence these effects. Starting with a low dose (0.5–1mg) and taking it 30–60 minutes before bed can help minimise risks. Avoid alcohol, and consult your GP if side effects persist or worsen. For severe symptoms, seek immediate medical attention.
Using melatonin responsibly under medical advice ensures safety and effectiveness.
What Are Side Effects of Melatonin? A Doctor Explains
Common Side Effects of Melatonin
Most people taking melatonin experience only mild and temporary side effects as their bodies adjust. Let’s take a closer look at these effects and how they can influence daily life.
Mild and Short-Term Side Effects
One of the most frequently reported side effects of melatonin is drowsiness. Since melatonin is designed to regulate sleep, it naturally promotes a sense of sleepiness. However, for some individuals, this sedative effect can linger into the following day, leading to grogginess. This highlights the importance of sticking to the dosage recommended by your GP.
Effects on Daily Activities
Daytime drowsiness can interfere with activities that demand focus and alertness. In clinical trials, 1.66% of participants reported experiencing daytime sleepiness after taking melatonin. While this may seem like a small percentage, the impact on daily tasks can still be noticeable.
The NHS advises against driving, cycling, or operating machinery if you feel sleepy or dizzy after taking melatonin. In the UK, it’s illegal to drive if medication affects your ability to do so safely.
Certain factors can make daytime drowsiness more likely. These include taking higher doses, using extended-release formulations, or being older. Dr Dustin Cotliar, a sleep medicine specialist, explains:
"Most people end up taking a dose of melatonin that is unnecessarily high through no fault of their own due to formulations stocked on shelves. For most people, 1-3 mgs is more than enough and is just as effective as higher doses, but with less risk of side effects."
If daytime drowsiness persists, there are steps you can take to minimise it. Avoid consuming alcohol, as it amplifies melatonin’s sedative effects, making it harder to stay alert during the day. Similarly, certain medications and herbal remedies with sedative properties may intensify drowsiness.
Timing also plays a crucial role. Taking melatonin too late in the evening or at an inappropriate time can cause its effects to carry over into the next day, potentially disrupting work, school, or other responsibilities. Being mindful of these immediate effects can help you manage melatonin use effectively before considering rarer, more severe side effects.
Rare and Serious Side Effects
While most people only experience mild side effects from melatonin, there is a small chance of rare but serious reactions. According to NHS guidance, fewer than 1 in 1,000 people may encounter these severe side effects. Being able to recognise these symptoms early is essential for your safety.
Identifying Severe Symptoms
Certain warning signs demand urgent medical attention. These include blurred vision, fainting, confusion, dizziness, or vertigo. Additionally, any unexplained or persistent bleeding, bruising, or blood in the urine should be immediately evaluated.
Changes in mood, such as feeling unusually low or sad after starting melatonin, might also signal a serious reaction.
One of the most critical risks is anaphylaxis, a life-threatening allergic reaction. Symptoms include sudden swelling (particularly of the lips, mouth, throat, or tongue), difficulty breathing, a tight throat, or changes in skin colour (such as blue, grey, or pale tones). In such cases, call 999 without delay.
Other severe signs to watch for include excessive drowsiness, confusion, or being unresponsive. In children, look out for unusual limpness, floppiness, or difficulty focusing, such as an inability to lift their head.
A rash that is swollen, raised, itchy, blistered, or peeling should also be reviewed by a medical professional.
When to Contact Your GP
If you experience any of these severe symptoms, contact your GP or call 111 immediately. Keeping a detailed record of the side effects can assist your healthcare provider in adjusting your treatment plan effectively.
Factors That Affect Side Effects
Understanding what influences melatonin's side effects can help you use it more safely and effectively. Several factors determine whether you'll experience side effects and how intense they might be.
Dosage and Product Type
The dose of melatonin you take plays a big role in the likelihood of side effects. Higher doses are more likely to cause drowsiness, headaches, or stomach discomfort. Starting with a low dose - typically 0.5mg to 1mg - about 30 minutes before bed can reduce these risks.
Extended-release formulations work differently from immediate-release tablets. While they provide a steady release of melatonin throughout the night, they can sometimes leave you feeling groggy the next morning. If you notice this, switching to an immediate-release option might better suit your sleep needs.
Timing also matters. Taking melatonin too early could make you feel sleepy before you're ready for bed, while taking it too late might leave you feeling sluggish the next day.
The quality of the product is another factor. Some supplements may have inconsistent or unverified melatonin concentrations, which can lead to unexpected side effects. Opting for products that have undergone independent testing can provide more reliable results.
Age and Health Conditions
Your age and overall health can significantly impact how your body processes melatonin.
Older adults metabolise melatonin at a slower rate, which may lead to prolonged drowsiness or an increased risk of falls and confusion during the night. On the other hand, children and teenagers are often more sensitive to melatonin, sometimes experiencing mood changes or vivid dreams.
Certain health conditions can also heighten the risk of side effects. For example, if you have liver problems, your body may struggle to break down melatonin efficiently, leading to stronger or longer-lasting effects. Similarly, kidney disease can slow the clearance of melatonin from your system.
People with autoimmune conditions like rheumatoid arthritis or multiple sclerosis should be cautious, as melatonin can influence immune system activity and potentially affect their symptoms.
Mental health conditions such as depression or anxiety disorders can also complicate melatonin use. While improved sleep might help some individuals feel better, others may notice a worsening of their symptoms, especially if they're already taking medication for these conditions.
Drug Interactions
Melatonin can interact with a variety of medications, potentially altering their effects or increasing side effects. If you're in the UK, some common medications to watch out for include:
- Anticoagulants like warfarin: Melatonin may enhance their blood-thinning effects, increasing the risk of bleeding. If you're on warfarin, your GP may need to monitor your INR levels more closely.
- Sedatives and sleeping tablets: Combining these with melatonin can lead to excessive drowsiness, confusion, or difficulty waking up. Medications like diazepam, temazepam, and zopiclone are particularly notable.
- Antihypertensive medications: Melatonin may either enhance or reduce the effectiveness of blood pressure treatments. Beta-blockers like propranolol are especially prone to interactions.
- Antidepressants, particularly SSRIs like sertraline or citalopram: These can affect how your body naturally produces and uses melatonin, potentially altering the effectiveness of either the antidepressant or the melatonin supplement.
- Diabetes medications: Melatonin can sometimes cause changes in blood sugar levels, which may require adjustments to insulin or other diabetes treatments.
- Immunosuppressive drugs: Used after organ transplants or for autoimmune conditions, these medications may be affected by melatonin's impact on the immune system, potentially reducing their effectiveness.
Always let your pharmacist know about all the medications and supplements you’re using, including over-the-counter remedies and herbal products. They can help identify any potential interactions and advise whether melatonin is suitable for your situation. Being informed and seeking professional guidance is key to using melatonin safely.
How to Reduce Side Effects
Here’s how you can minimise melatonin side effects by following some practical steps.
Safe Usage Guidelines
Take melatonin 30–60 minutes before bedtime in a dimly lit, cool room (16°C–19°C), free from screens. This helps align the supplement with your natural sleep cycle.
Avoid alcohol when taking melatonin. Alcohol disrupts sleep patterns and can heighten melatonin's sedative effects, causing excessive drowsiness or confusion.
Refrain from driving or operating machinery after taking melatonin. Its effects can last for hours and may be unpredictable, so plan your evening to avoid any activities requiring alertness.
Do not take melatonin during the day unless advised by a healthcare professional, such as for jet lag. Using it in daylight can disrupt your circadian rhythm and worsen sleep issues.
Adjusting Your Dosage
Finding the right dose often takes some trial and adjustment. Start with the lowest effective dose, usually between 0.5mg and 1mg, and stick with it for at least a week before considering an increase. Many people find smaller doses work better.
If side effects like headaches or stomach upset occur, reduce your dose by half and monitor how you feel. Even 0.25mg can be effective, particularly for older adults who metabolise melatonin more slowly.
If sleep doesn’t improve, increase the dose gradually. Move up in small steps - such as from 1mg to 1.5mg, then 2mg if needed. Doses above 3mg rarely offer added benefits and increase the risk of side effects.
Adjust the timing before increasing the dose. If morning grogginess is an issue, try taking your current dose 15 minutes earlier rather than increasing it. This simple tweak often reduces next-day fatigue.
Keep a two-week sleep diary while adjusting your dose. Record the amount taken, the time of administration, how quickly you fell asleep, sleep quality, and any side effects. This can help you identify patterns and find the optimal dose faster.
Switch formulations if necessary. If extended-release tablets leave you feeling groggy, try immediate-release versions. Alternatively, if you fall asleep easily but wake during the night, an extended-release formula may help, even if it initially causes morning drowsiness.
If these adjustments don’t resolve side effects, professional advice is your next step.
Getting Professional Advice
If self-adjustments don’t improve your experience, professional guidance can help.
Speak to your GP if side effects last more than a week or interfere with daily life. Persistent headaches, digestive issues, mood changes, or excessive daytime sleepiness may require medical attention.
Seek urgent care if you experience severe symptoms like chest pain, difficulty breathing, dizziness, or signs of an allergic reaction (rash, swelling). These symptoms need immediate evaluation.
Talk to your pharmacist before starting melatonin if you’re on other medications. They can check for potential interactions, especially with blood thinners, blood pressure medications, or antidepressants.
If you take multiple supplements or have chronic conditions, consult your GP for a medication review. They can determine if melatonin is suitable for you or suggest alternatives.
Consider a specialist referral if sleep problems persist despite proper melatonin use. Your GP can refer you to an NHS sleep clinic, where experts can investigate and address underlying sleep disorders.
Use trusted sources for products and information. Platforms like Buy Melatonin offer quality supplements and advice tailored to UK standards.
Consult your GP if sleep issues continue despite adjustments. Sometimes, improving sleep hygiene or treating conditions like sleep apnoea can be more effective than relying on supplements.
Conclusion
Understanding the potential side effects of melatonin is key to using it safely and effectively. For most people, any side effects - such as drowsiness, mild headaches, or slight stomach discomfort - are usually temporary and manageable.
To reduce the chances of experiencing these side effects, start with the lowest effective dose (around 0.5–1mg) about 30–60 minutes before bedtime. Ensure you’re in a calm, suitable environment, as factors like age, overall health, and other medications can influence how your body reacts to melatonin.
If side effects persist for more than a week or begin to disrupt your daily life, it’s important to consult your GP. They can assess whether melatonin is appropriate for your circumstances, check for any possible interactions with other medications, and recommend alternatives if necessary. For severe symptoms - such as chest pain, difficulty breathing, or signs of an allergic reaction - seek immediate medical attention.
Pay attention to how your body responds and adjust the dosage or timing as needed. Many people find that small changes can resolve minor issues without the need for professional help. By taking these precautions, you can use melatonin as a helpful addition to your sleep routine.
While melatonin can be effective for improving sleep, it isn’t the right solution for everyone. If problems persist or worsen, always seek guidance from your GP. Following their advice will help you get the most out of melatonin while keeping any risks to your health at a minimum.
FAQs
How can I find the right melatonin dosage for my needs?
The right amount of melatonin can differ from one person to another. For most adults, starting with 1 to 3 milligrams about 30 minutes before bedtime is typical. If you're using melatonin to manage jet lag, a dose of around 3 milligrams once a day for up to five days after arriving at your destination is often suggested.
It's wise to begin with the smallest effective dose and adjust as needed. Be sure to consult a healthcare professional before changing your dosage, particularly if you have existing health conditions or are on other medications.
What should I do if I have serious side effects from taking melatonin?
If you notice severe side effects after taking melatonin - such as blurred vision, fainting, confusion, intense dizziness, or symptoms of an allergic reaction like swelling, a rash, or difficulty breathing - stop using it straight away and seek urgent medical help. Contact emergency services or head to the nearest hospital for immediate care.
Additionally, make an appointment with your GP as soon as possible to discuss these symptoms and determine whether melatonin is appropriate for you. Your well-being should always be the top priority, so never overlook serious or unexpected reactions.
Are there health conditions that make melatonin unsafe to use?
Certain health conditions can make using melatonin less safe or increase the likelihood of side effects. For instance, individuals dealing with bleeding disorders, depression, high blood pressure, or liver or kidney issues should approach melatonin with care. If you've previously had an allergic reaction to melatonin, it's best to avoid it entirely.
People with seizure disorders or those taking certain medications might also encounter risks, such as changes in mood or a higher chance of bleeding. To stay on the safe side, always speak with a healthcare professional before taking melatonin, particularly if you have existing medical conditions or are on any medication.