Understanding Melatonin and Its Function
Melatonin is a hormone your brain produces naturally in response to darkness, helping to regulate your body's circadian rhythm and sleep [1.7.1]. It is sold over-the-counter in the U.S. as a dietary supplement and is commonly used to address issues like jet lag and sleep disorders [1.4.3, 1.11.3]. However, because it's available without a prescription doesn't mean it's free from interactions [1.4.3]. Since the FDA regulates melatonin as a dietary supplement, its purity and dosage can vary significantly between products, with some containing much more melatonin than labeled or even other substances like serotonin [1.11.2, 1.11.3]. It's crucial to consult a healthcare provider before starting melatonin, especially if you are taking other medications.
Prescription Medications to Use with Caution
Several classes of prescription drugs can interact with melatonin, leading to increased side effects or reduced efficacy of the medication. Always inform your doctor about all medications and supplements you are taking.
Blood Thinners (Anticoagulants and Antiplatelet Drugs)
Mixing melatonin with medications that slow blood clotting, such as warfarin (Coumadin) or clopidogrel, can increase your risk of bleeding and bruising [1.2.1, 1.3.2]. Melatonin might enhance the effects of these drugs, so your doctor may need to monitor you more frequently or adjust your dosage [1.3.3].
Blood Pressure Medications
Melatonin can have a complicated relationship with blood pressure medications. It might worsen blood pressure for some people taking these drugs [1.4.1]. Specifically, melatonin can reduce the effectiveness of medications like nifedipine, a calcium channel blocker, potentially causing a rise in blood pressure [1.4.3]. Conversely, taking melatonin with other blood pressure drugs like beta-blockers or ACE inhibitors could cause blood pressure to drop too low (hypotension), especially in older adults [1.4.3].
Diabetes Medications
Melatonin can affect blood sugar levels [1.5.2, 1.5.3]. When taken with diabetes medications, there's a potential risk of blood sugar dropping too low (hypoglycemia) [1.5.4]. Although evidence is conflicting, it is recommended that individuals with diabetes monitor their blood sugar closely and consult their healthcare team before using melatonin [1.5.1, 1.5.4].
Immunosuppressants
Immunosuppressant medications work by decreasing the activity of your immune system, often used for autoimmune conditions or after an organ transplant [1.6.4]. Melatonin can stimulate immune function, which means it could interfere with and reduce the effectiveness of immunosuppressive therapy [1.6.1, 1.6.2].
Antidepressants
Interactions between melatonin and antidepressants vary. Some antidepressants, like fluvoxamine (Luvox) and selective serotonin reuptake inhibitors (SSRIs) like fluoxetine (Prozac), can increase melatonin levels in the body, leading to excessive drowsiness [1.2.1, 1.7.2]. In other cases, animal studies suggest melatonin might reduce the effectiveness of certain antidepressants [1.7.1]. There is also a risk of serotonin syndrome if a melatonin supplement is contaminated with serotonin and taken with an antidepressant [1.7.2].
Sedatives and CNS Depressants
Combining melatonin with other substances that cause drowsiness can lead to an additive sedative effect. This category includes:
- Benzodiazepines (e.g., diazepam, alprazolam) [1.2.3]
- Opioids (e.g., codeine, morphine) [1.2.2]
- Z-drugs for insomnia (e.g., zolpidem, zaleplon) [1.2.2]
- First-generation antihistamines (e.g., diphenhydramine/Benadryl) [1.2.3]
- Muscle relaxants [1.2.3] This combination can cause excessive drowsiness, impaired thinking, and increase the risk of a "hangover effect" the next day, which can make activities like driving dangerous [1.2.3].
Contraceptive Drugs
Birth control pills do not appear to be less effective when taken with melatonin [1.8.3]. However, contraceptive drugs can increase the body's natural melatonin levels. Taking a melatonin supplement in addition may heighten the hormone's effects and side effects, such as increased drowsiness, dizziness, and nausea [1.8.2, 1.8.3].
Anticonvulsants (Seizure Medications)
Melatonin may inhibit the effects of anticonvulsant medications and potentially increase the frequency of seizures, particularly in children with neurological disabilities [1.2.1]. It might also increase the risk of seizures when taken with other drugs that lower the seizure threshold [1.10.3].
Other Substances and Supplements
Alcohol
Experts strongly recommend against mixing alcohol and melatonin [1.9.1]. Both are central nervous system depressants, and combining them can lead to increased drowsiness, dizziness, breathing difficulties, and impaired motor control [1.9.1, 1.9.3]. Alcohol also disrupts natural sleep patterns and can reduce the body's own production of melatonin, potentially negating the supplement's purpose [1.9.2, 1.9.3].
Caffeine
Caffeine has the opposite effect of melatonin, promoting wakefulness. Consuming caffeine, especially within six hours of bedtime, can disrupt sleep [1.2.3]. Furthermore, caffeine can inhibit the enzyme that breaks down melatonin, which could more than double melatonin levels in the body if taken together [1.2.3, 1.10.1].
Herbal Supplements
Caution is advised when mixing melatonin with other herbal supplements, especially those that also cause sleepiness, such as valerian root and St. John's wort [1.12.1, 1.12.3]. Combining them can amplify the sedative effects of melatonin [1.12.2]. There is not enough research to confirm the safety of taking melatonin with other non-drowsy herbal remedies [1.12.1].
Melatonin Interaction Comparison Table
| Interacting Substance/Drug Class | Potential Interaction Effect | Risk Level |
|---|---|---|
| Blood Thinners (e.g., Warfarin) | Increased risk of bleeding and bruising [1.2.1, 1.3.2]. | Moderate to High |
| Blood Pressure Medications | May worsen or lower blood pressure unpredictably; can reduce the effectiveness of certain drugs like nifedipine [1.4.1, 1.4.3]. | Moderate |
| Diabetes Medications | Risk of hypoglycemia (low blood sugar) [1.5.2, 1.5.4]. | Moderate |
| Immunosuppressants | May interfere with and reduce the effectiveness of the medication [1.6.1, 1.6.4]. | High |
| Sedatives / CNS Depressants | Additive sedative effect, excessive drowsiness, impaired thinking [1.2.3]. | High |
| Alcohol | Greatly increased drowsiness, dizziness, and risk of breathing difficulties [1.9.1, 1.9.3]. | High |
| Antidepressants (e.g., Fluvoxamine) | Increased melatonin levels, leading to excessive drowsiness [1.2.1, 1.7.2]. | Moderate |
| Contraceptive Drugs | May increase side effects of melatonin like drowsiness and dizziness [1.8.2, 1.8.3]. | Low to Moderate |
| Caffeine | Can increase melatonin levels and interfere with sleep [1.2.3, 1.10.4]. | Low |
Conclusion
While melatonin is a popular and accessible sleep aid, it is not without risks, especially when combined with other medications and substances. Its interactions can range from mild drowsiness to more serious issues like increased bleeding risk or interference with life-sustaining medications. The lack of strict FDA regulation over supplements also means that the purity and dosage of commercial melatonin can be inconsistent [1.11.2]. Therefore, it is essential to consult a healthcare professional before adding melatonin to your routine to ensure it is safe for you. For more information on supplement safety, you can visit the National Institutes of Health (NIH) website.
