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Moderate evidenceGeneral health

Sulforaphane (Broccoli Extract)

The best-evidenced Nrf2 activator available, with genuine human data showing accelerated detoxification of airborne carcinogens. The health-outcome claims (cancer, autism, schizophrenia) are much weaker, and most products on the shelf deliver far less active compound than the label implies.

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What the science says

  • Carcinogen detoxification Moderate evidence

    In a randomized trial of 291 adults in Qidong, China, a broccoli sprout beverage produced a rapid, sustained and dose-dependent increase in urinary excretion of the benzene detoxication product S-phenylmercapturic acid (a 61% increase at the higher glucoraphanin/sulforaphane dose) along with increased acrolein conjugate excretion. This is a real, replicated pharmacodynamic effect in humans, mediated by Nrf2-driven phase II enzyme induction.

  • Schizophrenia and psychiatric symptoms Limited evidence

    A 2025 systematic review and meta-analysis of sulforaphane RCTs in schizophrenia found the trials small and heterogeneous, with no reliable improvement in total psychotic symptom scores; any signal was confined to secondary cognitive measures. Not a treatment.

  • Autism spectrum disorder Limited evidence

    The widely publicized 2014 Singh trial (44 young men, 18 weeks) reported improvements in behavioural rating scales, but subsequent larger and better-controlled replications have been inconsistent or null, and a 2022 network meta-analysis of supplement treatments for ASD did not find sulforaphane to be a reliably effective option. Evidence is preliminary at best.

  • Cancer prevention Limited evidence

    Human data are limited to biomarker endpoints — enzyme induction, histone deacetylase inhibition in blood cells, modest PSA changes in small prostate studies. No trial has shown reduced cancer incidence or recurrence. The observational link between cruciferous vegetable intake and lower cancer risk is not evidence that an isolated extract does the same.

Dosage & safety

Studied doseTrials have used broccoli sprout preparations supplying roughly 10-100 mg sulforaphane or 100-800 micromol glucoraphanin per day. Critically, most supplements contain glucoraphanin (the inert precursor) and rely on the enzyme myrosinase to convert it — many products either lack active myrosinase or are taken by people whose gut bacteria convert it poorly, yielding under 10% conversion. Choose a product standardized to stabilized sulforaphane or one that explicitly includes active myrosinase, and avoid taking it with hot liquids, which destroy the enzyme.
SafetyGenerally well tolerated; the most common effects are gas, bloating, dyspepsia and a sulfurous odour, and mild nausea at higher doses. Broccoli sprouts are goitrogenic in principle (thiocyanate can compete with iodine uptake), so people with iodine deficiency or thyroid disease should not take very high doses long term. Raw sprout products carry a real risk of bacterial contamination (Salmonella, E. coli) and should be avoided by pregnant, immunocompromised or elderly people. Sulforaphane is an Nrf2 activator; because Nrf2 activation can also protect tumour cells, avoid during active chemotherapy without oncologist input. No adequate pregnancy or lactation data for concentrated extracts.

How to take it

TimingTiming does not matter; take it daily.
With food?With food, but never with a hot drink — heat destroys the myrosinase enzyme that converts glucoraphanin to sulforaphane.
Worth knowingIf the label lists glucoraphanin with no active myrosinase, conversion can fall below 10% — choose stabilised sulforaphane or a product that explicitly adds the enzyme.

Interactions

With medications

  • chemotherapy

    Sulforaphane activates Nrf2, which can also protect tumour cells from treatment. do not use during active chemotherapy without oncologist input

  • levothyroxine and thyroid treatment

    Thiocyanate from brassica compounds competes with iodine uptake, which matters at high chronic doses. avoid very high long-term doses if you have thyroid disease or low iodine intake, and discuss it with your doctor

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

What is sulforaphane good for?

Sulforaphane's best evidence (moderate) is for speeding detoxification of airborne carcinogens: in a trial of 291 adults, a broccoli sprout drink increased urinary excretion of a benzene breakdown product by up to 61%. Claims for cancer prevention, autism and schizophrenia are much weaker.

Does sulforaphane help autism?

The evidence is limited: a 2014 trial in 44 young men reported behavioural improvements, but larger replications were inconsistent or null. A 2022 network meta-analysis did not find sulforaphane a reliably effective option for autism.

How do I choose a sulforaphane supplement that works?

Choose stabilised sulforaphane or a product that explicitly adds active myrosinase; glucoraphanin without the enzyme can convert at under 10%. Never take sulforaphane with a hot drink, since heat destroys myrosinase.

Does sulforaphane affect the thyroid?

Broccoli sprout compounds can compete with iodine uptake, so avoid very high long-term sulforaphane doses if you have thyroid disease or low iodine intake. Also avoid sulforaphane during active chemotherapy without oncologist input.

Scientific references

Where to buy

Swanson Vitamins, Sulforaphane from Broccoli Sprout Extract, 400 mcg, 60 Vegan Caps

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