Is St John's Wort legal to buy in Australia?

Yes. St John's Wort preparations are widely available over the counter in Australia as listed complementary medicines on the Australian Register of Therapeutic Goods (ARTG). They are not scheduled under the Poisons Standard in a way that restricts consumer access, though all compliant products must carry TGA-mandated interaction warnings on their labels.

What are the main active constituents in St John's Wort?

The most studied constituents are hypericin and pseudohypericin (naphthodianthrones, responsible for the red colouration in the flowers), and hyperforin (a phloroglucinol). Flavonoids including quercetin, kaempferol and amentoflavone are also present in significant concentrations and have been investigated for their own receptor interactions. The relative contribution of each class to the plant's overall pharmacological activity remains an active area of research.

Why does St John's Wort interact with so many medications?

Primarily because hyperforin is a potent inducer of the CYP3A4 enzyme system and P-glycoprotein, both of which are central to how the body metabolises a large number of medicines. When these pathways are induced, plasma concentrations of co-administered drugs — including ciclosporin, warfarin, oral contraceptives and antiretrovirals — can fall significantly, with serious clinical consequences. The TGA has published specific guidance on this interaction profile.

Can St John's Wort products make therapeutic claims on their label in Australia?

No. Listed complementary medicines on the ARTG may only use permitted indications drawn from the TGA's published schedule of pre-approved general wellbeing statements. Disease treatment or relief claims are not permitted for listed products. Products making claims outside these boundaries can be subject to TGA enforcement action under the Therapeutic Goods Act 1989.

How are St John's Wort extracts standardised, and does standardisation guarantee consistency?

Most commercial extracts are standardised to a marker compound — typically 0.3% hypericin or, in some newer products, 3–5% hyperforin. Standardisation improves batch-to-batch consistency for those specific markers, but does not control the full phytochemical profile of the extract. Seasonal variation, growing conditions, solvent choice and processing methods all affect the minor-constituent landscape. This is a recognised limitation when comparing different products or interpreting clinical trial data conducted with a specific historical extract.

St John’s Wort: Traditional Use, Constituents and Evidence

By Naomi Ellison · 22 April 2026 · 7 min read

My nan kept Hypericum perforatum growing along the back fence , the same narrow beds where the lemon balm and calendula lived. She called it "chase-devil," which is an old English folk name, and she dried the flowering tops every January without a great deal of ceremony. I didn't think much of it as a kid. Now, having spent years reading through 19th-century herbal literature and more recent phytochemical data, I find the plant genuinely fascinating , not because it's simple, but because it isn't.

St John's Wort is one of the most studied phytomedicines on the planet. That's worth saying clearly, because a lot of plant medicines arrive on the research stage with one or two small trials and a lot of hype. This one has decades of clinical literature, a complex and well-characterised chemistry, a documented interaction profile that demands respect, and a regulatory status in Australia that's worth understanding before you assume it's just a shelf herb.

A brief history of Hypericum perforatum

The genus name Hypericum likely derives from the Greek hyper (above) and eikon (image), linking the plant to traditions of hanging it above doorways to ward off evil spirits around the feast of St John the Baptist , hence the common name. European herbalists from Dioscorides onward documented it for wounds, burns and what we might now loosely call melancholic states. John Gerard's Herball of 1597 describes a distilled oil preparation, and Nicholas Culpeper's 1653 Complete Herbal lists it for a long catalogue of complaints.

European colonists brought H. perforatum to Australia, and it naturalised so aggressively across Victoria, New South Wales and South Australia that it's now listed as a noxious weed under state legislation in several jurisdictions. There's a certain irony there; a plant historically revered as medicine becoming a declared pest on the very continent that imported it. If you're foraging in the Adelaide Hills or the Grampians, you'll find it easily enough along roadsides and disturbed ground, bright yellow flowers facing upward in December and January. The translucent oil glands in the leaves are visible if you hold them to light, which is the plant's most useful field identification feature.

Key constituents and their chemistry

The phytochemistry of H. perforatum is reasonably well mapped at this point. Several constituent classes are considered pharmacologically relevant.

Naphthodianthrones: Hypericin and pseudohypericin are the red-pigmented compounds found in the dark glands of the flower petals and, to a lesser extent, the leaves. They are arguably the most studied constituents. Standardised extracts used in clinical research are typically standardised to 0.3% hypericin, which became an early convention in European trials, though whether hypericin is itself the primary active compound or simply a convenient marker is still debated in the literature.

Phloroglucinols: Hyperforin is a bicyclic phloroglucinol that has attracted significant research attention over the past two decades. It inhibits the reuptake of several neurotransmitters including serotonin, dopamine and noradrenaline via a sodium-conductive mechanism that is mechanistically distinct from conventional synthetic reuptake inhibitors. Some researchers consider hyperforin the constituent most responsible for the plant's psychotropic activity, though isolated-constituent models don't capture whole-plant complexity particularly well.

Flavonoids and xanthones: Quercetin, kaempferol, luteolin and I3,II8-biapigenin (amentoflavone) are present in meaningful concentrations. These interact with various receptor systems. Amentoflavone in particular has been shown in vitro to bind at GABA-A receptors and has some affinity at cannabinoid receptor sites, which is a thread that occasionally appears in phytocannabinoid-adjacent literature given interest in the endocannabinoid system and modulating compounds from plant sources.

Terpenes: H. perforatum essential oil contains a range of volatile terpenoids including alpha-pinene, beta-caryophyllene and traces of myrcene, though these are present in far lower concentrations than in cannabis preparations and are not considered primary contributors to effect in standard oral formulations.

Whole-plant extracts contain all of these simultaneously, and the interaction between constituent classes is not fully resolved. This is a recurring challenge in phytomedicine research generally; the tendency to isolate individual molecules for study can miss the complexity of the matrix they come from.

What the clinical research actually shows

The evidence base for H. perforatum is largest in the area of mood-related outcomes, particularly mild to moderate presentations. A 2008 Cochrane systematic review by Linde et al., drawing on 29 randomised trials and over 5,000 participants, found standardised extracts were more effective than placebo in the trial populations studied, and comparable to standard antidepressants for mild to moderate presentations, with a somewhat more favourable reported adverse-effect profile in those trials. The review also noted that evidence in severe presentations was weaker and less consistent.

The short version is: the clinical literature is more substantial than for most plant medicines, but it is not without methodological limitations. Trial heterogeneity is significant. Extract standardisation varies between manufacturers. Placebo response rates in mood trials are notoriously high, which complicates interpretation. And most trials are relatively short-term, so long-run safety data from controlled studies is limited.

I'd argue that some popular summaries of this research go further than the data warrants; presenting the evidence as more settled than it is. The honest reading is "promising, reasonably well-evidenced for specific populations in short-term trials, with important caveats." That's not nothing, but it's not a clean bill of health either.

Drug interactions: the pharmacokinetic problem

This is where St John's Wort gets genuinely serious. Hyperforin is a potent inducer of CYP3A4 and P-glycoprotein, two of the body's primary drug-metabolising systems. The consequences for co-administered medicines are well documented and clinically significant. Pharmacokinetic studies have demonstrated substantially reduced plasma concentrations of ciclosporin (an organ transplant rejection drug), antiretroviral agents, warfarin, oral contraceptives, and certain anticonvulsants in patients taking H. perforatum extracts concurrently.

This is not a theoretical concern, there are documented case reports of transplant rejection and unintended pregnancy attributed to these interactions. The TGA has issued regulatory guidance on this. Any preparation containing H. perforatum that is listed or registered on the Australian Register of Therapeutic Goods (ARTG) is required to carry mandatory warnings about interactions with prescription medicines, and the TGA's advisory committee guidance recommends that practitioners be informed before use alongside any narrow-therapeutic-index drug.

Australian regulatory status

In Australia, St John's Wort preparations are primarily regulated as listed complementary medicines on the ARTG. Listing (as opposed to registration) relies on a self-assessed quality and safety dossier; the TGA does not independently evaluate listed products for efficacy before listing. Manufacturers must comply with Good Manufacturing Practice standards, and permitted indications are drawn from a restricted schedule of pre-approved claims, these are general wellbeing statements, not disease treatment claims.

Because of the interaction profile, some higher-dose or standardised products have attracted closer scrutiny. Products making claims beyond the ARTG-permitted indications can be subject to enforcement action. The TGA's Complementary Medicines regulatory framework and the Therapeutic Goods (Permitted Indications) instrument set the boundary for what can legally be stated on a label or in advertising.

H. perforatum is not scheduled under the Poisons Standard in the same way that, say, kava preparations face import controls under the Customs (Prohibited Imports) Regulations, or psilocybin sits as a Schedule 9 prohibited substance except under specific Authorised Prescriber pathways. St John's Wort over-the-counter products are widely available. But "widely available" does not mean without regulatory oversight, and the interaction warnings on compliant products exist for good reason.

What standardisation does and doesn't capture

One thing that rarely gets enough attention in popular writing about this plant: standardisation to 0.3% hypericin or 3–5% hyperforin tells you something about those specific markers, but says very little about the full flavonoid and terpenoid profile of any given batch. Seasonal variation, growing conditions, extraction method and solvent all shift the minor-constituent landscape considerably. A standardised extract is more consistent than a raw dried herb; but it is not a single defined chemical entity in the way a synthetic pharmaceutical is.

This matters for interpreting trial data, because a product used in a 1990s German clinical trial and a product on an Adelaide health-food shelf today may share a hypericin number on the label while differing quite substantially in their broader chemistry. It's worth keeping that in mind when reading both the enthusiastic and the sceptical literature on the plant.

Sources

, Naomi Ellison, Botanical & phytomedicine writer

Common questions

Is St John's Wort legal to buy in Australia?: Yes. St John's Wort preparations are widely available over the counter in Australia as listed complementary medicines on the Australian Register of Therapeutic Goods (ARTG). They are not scheduled under the Poisons Standard in a way that restricts consumer access, though all compliant products must carry TGA-mandated interaction warnings on their labels.
What are the main active constituents in St John's Wort?: The most studied constituents are hypericin and pseudohypericin (naphthodianthrones, responsible for the red colouration in the flowers), and hyperforin (a phloroglucinol). Flavonoids including quercetin, kaempferol and amentoflavone are also present in significant concentrations and have been investigated for their own receptor interactions. The relative contribution of each class to the plant's overall pharmacological activity remains an active area of research.
Why does St John's Wort interact with so many medications?: Primarily because hyperforin is a potent inducer of the CYP3A4 enzyme system and P-glycoprotein, both of which are central to how the body metabolises a large number of medicines. When these pathways are induced, plasma concentrations of co-administered drugs — including ciclosporin, warfarin, oral contraceptives and antiretrovirals — can fall significantly, with serious clinical consequences. The TGA has published specific guidance on this interaction profile.
Can St John's Wort products make therapeutic claims on their label in Australia?: No. Listed complementary medicines on the ARTG may only use permitted indications drawn from the TGA's published schedule of pre-approved general wellbeing statements. Disease treatment or relief claims are not permitted for listed products. Products making claims outside these boundaries can be subject to TGA enforcement action under the Therapeutic Goods Act 1989.
How are St John's Wort extracts standardised, and does standardisation guarantee consistency?: Most commercial extracts are standardised to a marker compound — typically 0.3% hypericin or, in some newer products, 3–5% hyperforin. Standardisation improves batch-to-batch consistency for those specific markers, but does not control the full phytochemical profile of the extract. Seasonal variation, growing conditions, solvent choice and processing methods all affect the minor-constituent landscape. This is a recognised limitation when comparing different products or interpreting clinical trial data conducted with a specific historical extract.