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A plain-language summary of the cited sources below. Informational only — not medical advice.
Melatonin is a hormone that your body naturally produces to help regulate sleep. The medication form works by acting on two types of receptors in the brain — MT1 and MT2. The MT1 receptors help quiet down nerve activity, while the MT2 receptors help shift the body's internal clock. Together, these actions are thought to promote sleep. The medication is approved for short-term treatment of poor-quality sleep in people aged 55 and over, though it is also prescribed for insomnia more broadly.
Melatonin leaves the body relatively quickly, with a half-life of around three and a half to four hours. It's broken down in the liver by enzymes called CYP1A1, CYP1A2, and possibly CYP2C19. This means other medications that affect these enzymes could change how melatonin works in the body.
Side effects that have been reported include headache, cold-like symptoms in the nose and throat, back pain, joint pain, and diarrhoea. More serious reactions are possible but documented in the source material as including severe allergic reactions such as swelling under the skin or generalised hypersensitivity, fainting, chest pain related to reduced blood flow to the heart, and a drop in white blood cell count. The medication should not be used by anyone with a known allergy to any ingredient in the product.
Common off-label uses observed in AU practice — none of these are TGA-approved indications for this substance. If the documented purpose is one of these, the prescription falls outside the TGA-approved set and may sit inside the chemical-restraint frame depending on jurisdiction and context.
Insomnia Clinical criteria: Treatment Phase: Initial Patient must have Smith-Magenis Syndrome confirmed by genetic testing, AND The condition must be inadequately responsive to sleep hygiene measures, resulting in the patient experiencing a period of at least 12 consecutive weeks of impaired sleep (see definition of impaired sleep below). Treatment criteria: Must be treated by a medical practitioner identifying as at least one of: (i) a paediatrician, (ii) a sleep physician, (iii) neurologist, (iv) a psychiatrist, (v) a developmental specialist (see NOTE); this authority approval is being sought by one of these 5 prescriber types. Population criteria: Patient must be at least 2 years of age, but yet to turn 18 years of age, at treatment initiation with this drug. Definition: For the purposes of administering this restriction, Smith-Magenis Syndrome is confirmed by the deletion or variation of the retinoic acid induced 1 (RAI1) gene on chromosome 17p11.2 Definition:For the purposes of administering this restriction, impaired sleep is at least one of:(i) less than 6 hours of continuous sleep on at least 3 occasions over a given 5-day interval; (ii) taking at least half an hour to fall asleep on at least 3 occasions over a given 5-day interval. Prior to seeking authorisation for this pharmaceutical benefit, document the amount of continuous sleep/sleep latency in the patient's medical records for a period of 2 consecutive weeks, but ensure the impairment has been observed for at least 12 consecutive weeks. The documented values (averages) will form baseline measurements upon which the extent of response to treatment is to be considered under the Continuing treatment listing. The observations of continuous sleep/sleep latency may be based on any of the following, including a mix of: patient self-reporting, parental observation, documented medical history, sleep studies conducted by health professionals.
“The activity of melatonin at the MT1 MT2 receptors is believed to contribute to its sleep- promoting properties via their distinct actions on the circadian clock. The MT1 receptors are thought to inhibit neuronal firing, while the MT2 receptors have been implicated in the phase- shifting response.”
“Terminal half life (t½) is 3.5-4 hours.”
A plain-language summary of the cited sources below. Informational only — not medical advice.
Melatonin is an S4 melatonin receptor agonist approved for short-term treatment of primary insomnia characterised by poor sleep quality in patients aged 55 or over. Its sleep-promoting properties derive from activity at MT1 and MT2 receptors: MT1 receptors inhibit neuronal firing, while MT2 receptors mediate phase-shifting of the circadian clock. The terminal half-life is 3.5–4 hours.
Metabolism involves CYP1A1, CYP1A2, and possibly CYP2C19. Common adverse effects include headache, nasopharyngitis, back pain, arthralgia, and diarrhoea. Serious adverse effects reported include angioedema, hypersensitivity reactions, syncope, angina pectoris, and leukopenia. Melatonin is contraindicated in patients with known hypersensitivity to any ingredient of the product.
Working under the parallel aged-care framework? Aged-care equivalent →
These are practitioner observations, not TGA-approved indications. A use being off-label does not by itself imply a regulated restrictive practice; review the documented purpose against the observed function in context.
Curated subset. The full adverse-effect list is in the TGA Product Information; click any citation above to open it.
“Experimental data suggest that iso-enzymes CYP1A1, CYP1A2 and possibly CYP2C19 of the cytochrome P450 system are involved in melatonin metabolism.”