Minoxidil is a prodrug switched on by the enzyme SULT1A1. Birth control, green tea, turmeric, quercetin, and Tylenol all compete for that enzyme, but almost none of it has been tested on a real human scalp.
Minoxidil does nothing until your body switches it on. The molecule you apply or swallow is a prodrug; the active form is minoxidil sulfate, and to make it, an enzyme called SULT1A1 has to attach a sulfate group. No conversion, no active drug. That single step is why two people on the identical dose can get completely different results.
So the obvious next question, and the one people keep asking in the comments, is: can anything get in the way of that enzyme? The answer is yes in a test tube, and the list is more ordinary than you would guess. Your birth control competes for it. So does the green tea in your fat-burner, the turmeric in your joint stack, and the quercetin in your "DHT blocker."
The short answer: SULT1A1, the enzyme that activates minoxidil, is inhibited or competed for by several everyday things: ethinylestradiol in combined birth control (a potent nanomolar inhibitor), the EGCG in green tea, curcumin in turmeric, quercetin, and, through the shared sulfate pool, acetaminophen (Tylenol) and high-dose vitamin C. Aspirin is only a weak direct inhibitor, though one small study linked it to worse minoxidil response. Crucially, almost none of this has been tested for hair growth on a human scalp, most of it is enzyme chemistry in a dish or the liver, and none of it is a reason to stop a prescribed medication.
SULT1A1 can be slowed down three different ways, and they are not the same thing. Keeping them separate is the difference between an accurate claim and a scary one.
With that framing, here is what the evidence actually says, most real-world-relevant first.
In a test tube, yes. Ethinylestradiol, the estrogen in most combined oral contraceptives, is a potent SULT1A1 inhibitor, blocking it at low-nanomolar concentrations (Rohn 2012; Yasuda 2005). That is worth pausing on, because the group most likely to be on the pill, premenopausal women, is also a group with female-pattern hair loss.
It is the most relevant name on the list and it has real in-vitro potency. But it has never been shown to change a hair outcome in a person, and to be completely clear, it is not a reason to stop or change your contraception. It is a shared enzyme and an open question, nothing more.
Possibly in theory, not proven in practice. Acetaminophen works by the fuel route: it is heavily sulfated itself, so it draws down the sulfate pool the follicle needs. Notably, this is the one item with actual follicle data. In cultured hair follicles, acetaminophen blocked minoxidil's effect by scavenging the sulfate (Buhl 1990). Systemically, a single large dose measurably lowers the body's inorganic sulfate (Slattery 1987).
That is a real, follicle-level mechanism, but it was shown in mouse follicle culture at high concentrations, not in a person taking a normal dose. Treat it as a plausible interaction, not an established one.
Here the honest answer is more interesting than the meme, and it is the one the comments keep raising. As a direct SULT1A1 inhibitor, aspirin is weak, far weaker than the fenamate NSAIDs below, weak enough that on potency alone it barely belongs on the list. But there is a separate, real signal: a small study (Goren 2018, 24 subjects) found that low-dose aspirin users had lower measured follicular sulfotransferase activity and were predicted to respond worse to topical minoxidil.
It is a correlation from a small study with an unclear mechanism, not an established interaction. And aspirin is usually taken for cardiovascular protection, where the stakes are far higher than hair. This is a "mention it to your doctor," not a "stop your aspirin."
The isolated enzyme, yes, potently. The EGCG in green tea inhibits SULT1A1 at an allosteric site with a Ki around 34 nanomolar, and dietary intake can reach several times that in plasma (Cook 2016). Curcumin, from turmeric, inhibits it with an IC50 near 14 nanomolar and is relatively selective for SULT1A1 (Vietri 2003). Quercetin, the flavonoid in many "DHT blocker" supplements, is one of the most potent SULT1A1 inhibitors known, and, unusually, it was tested against minoxidil directly, blocking minoxidil sulfation in human liver cytosol at low-nanomolar concentrations (Eaton 1996; De Santi 2002).
These are genuinely potent inhibitors of the isolated enzyme, and quercetin is the strongest direct-to-minoxidil evidence in the group. All of it is test-tube and liver, never scalp.
For the record, one clarification the internet gets backwards: mefenamic acid, a fenamate used for menstrual pain, is a genuinely potent inhibitor (IC50 around 0.02 micromolar; Pacifici 2004; Wang 2017), but the everyday NSAIDs, ibuprofen and naproxen, are weak enough to be irrelevant here. "NSAIDs blunt minoxidil" is only true for the fenamates.
A couple of names circulate as SULT1A1 blockers that simply are not. Resveratrol is a substrate of SULT1A1, not a meaningful inhibitor of the minoxidil pathway. It gets sulfated itself; it does not block minoxidil's activation. Coffee polyphenols (chlorogenic and caffeic acid) are substrates too, not inhibitors. Your morning coffee is not blocking your minoxidil.
This is the part most "things killing your minoxidil" lists skip. Here is where each finding actually comes from, and none of it was a growing human hair:
| Where it was measured | Which items |
|---|---|
| A test tube (purified enzyme or human liver / cell lines) | birth control, green tea, turmeric, quercetin, mefenamic acid, vitamin C |
| An animal follicle (mouse) | acetaminophen |
| A small human clinical correlation | aspirin (Goren 2018, n=24) |
| A human scalp, measured for hair growth | none of them |
Not one of these has ever been tested for actual hair growth on a human head. Systemic or in-vitro inhibition does not automatically mean follicular failure. So treat the whole list as biologically plausible and clinically unproven.
Mostly no. SULT1A1 is a constitutive, largely non-inducible enzyme. Your level is set mostly by genetics, by how many copies of the gene you carry and which version you inherited. Retinoids like tretinoin are the only lever with any human-scalp data, and even that is a weak, single-group signal measured as enzyme activity rather than hair. Two things people commonly claim raise it do not: vitamin D raises a different enzyme entirely (SULT2B1b), and sulforaphane is not part of the pathway that would raise SULT1A1 at all.
If topical minoxidil has never done much for you, the bigger question is usually whether your scalp activates it at all, which is a different story we cover in why minoxidil works for some people and not others. And if you want to understand what minoxidil does once it is switched on, see how minoxidil actually works at the follicle. Not sure where you fall? Take the hair quiz or see treatment options.
In a test tube, yes. Ethinylestradiol, the estrogen in most combined pills, is a potent SULT1A1 inhibitor at low-nanomolar concentrations (Rohn 2012), and SULT1A1 is the enzyme that activates minoxidil. It has never been shown to change a hair outcome in a person, and it is not a reason to stop or change your contraception.
Aspirin is a weak direct inhibitor of SULT1A1. But one small study of 24 people (Goren 2018) linked low-dose aspirin to lower follicular sulfotransferase activity and a worse predicted minoxidil response. That is a small correlation with an unclear mechanism, and aspirin's cardiovascular benefit outweighs hair, so it is not a reason to stop it.
Possibly in theory, not proven in practice. Acetaminophen is heavily sulfated and draws down the sulfate pool the follicle needs to activate minoxidil; it blocked minoxidil in cultured follicles (Buhl 1990) and depletes body sulfate at high doses (Slattery 1987). No study shows a normal Tylenol dose reduces hair regrowth in a person.
They are potent inhibitors of the isolated enzyme. Green tea EGCG blocks SULT1A1 with a Ki around 34 nanomolar (Cook 2016), and quercetin blocks minoxidil sulfation directly in human liver cytosol at low-nanomolar levels (Eaton 1996). Neither has been tested in a human scalp at achievable supplement doses, so treat it as plausible, not proven.
No. Coffee polyphenols (chlorogenic and caffeic acid) are substrates of SULT1A1, not inhibitors, meaning they get sulfated themselves rather than blocking minoxidil's activation. Your morning coffee is not blocking your minoxidil. Resveratrol is also a substrate, not a blocker, despite often being listed as one.
No. Nothing on this list has been shown to reduce hair growth in a person, and the highest-stakes items, birth control and aspirin, are taken for reasons far more important than hair. Spacing a supplement away from your dose is harmless, but stopping or changing a prescribed drug is a decision for your doctor, not a hair hack.
This article is for educational purposes only and is not medical advice. The enzyme interactions described here are, in almost every case, demonstrated only in laboratory or systemic settings and have not been shown to change hair outcomes in people. Do not start, stop, or change any medication, including over-the-counter drugs and supplements, based on this article. Talk to your physician or dermatologist.