Vitex (chasteberry): what it is and whether it helps PMS

Vitex agnus-castus is a shrub, and its common names are chasteberry, chaste tree, and vitex. Its dried fruit, the vitex berry, has been used for centuries; monks once used it as a pepper substitute, which is where the name monk's pepper comes from (Chasteberry, American Family Physician, 2005).

For roughly the last 50 years, extracts of that berry have been sold to treat premenstrual symptoms, especially breast tenderness before a period. You'll see it labeled as vitex, chasteberry, vitex agnus-castus, vitex castus, or agnus vitex. These are all names for the same plant extract, sold as capsules, tablets, or liquid tinctures.

Most research uses a standardized extract rather than raw berries, and one of the most studied is a proprietary preparation called BNO 1095. That matters because results from one brand's extract don't automatically transfer to another product with a different strength or preparation.

Scientists think vitex works mainly through dopamine. Compounds in the extract, called diterpenes, bind to D2 dopamine receptors on cells in the pituitary gland.

That binding lowers release of prolactin, a hormone that spikes more than usual in some people during stress or deep sleep in the days before a period. This extra prolactin release is one known cause of premenstrual breast tenderness, or mastalgia, so dampening it is the clearest mechanism behind vitex's effect on that symptom.

The same dopamine pathway may explain why vitex occasionally affects mood, including the rare side effects covered further down this page. Beyond the prolactin link, researchers haven't identified a separate, well-established mechanism for any effect of vitex on mood swings or irritability before a period.

Vitex is used most often for premenstrual syndrome and for cyclical breast pain that shows up before a period and eases once it starts. A 2005 review in American Family Physician concluded that current evidence supports chasteberry for breast discomfort and PMS, while evidence for menstrual irregularities and fertility problems is weak.

It's also marketed for very different uses, like boosting breast milk supply or lowering sex drive, but that same review found no real clinical support for either claim.

If your main complaint is sore, tender breasts before your period, vitex has the most consistent trial support of any of its traditional uses. For anything else it's marketed for, treat the claim as unproven until a doctor or a specific study says otherwise.

For PMS, the trial evidence is larger than for most supplements, but it's messy. A 2017 systematic review pooled 14 randomized trials and found a large average effect compared with placebo, but the studies disagreed heavily with each other, and patterns in the data suggested that smaller, lower-quality trials were more likely to get published, which can inflate the overall average (European Psychiatry, 2017).

A 2022 systematic review of 15 trials in 1,211 women found vitex reduced overall PMS symptom scores, with the biggest improvement in physical symptoms. The mood-symptom subgroup improved less, and that result wasn't clearly distinguishable from no effect (Pharmaceuticals, 2022). In plain terms, vitex's best-supported use is still physical, especially breast tenderness, rather than mood.

For PMDD specifically, trials have mostly enrolled women with PMS rather than a confirmed PMDD diagnosis, so there isn't a solid evidence base yet for vitex and PMDD mood symptoms. Niyora is a PMS and PMDD support app. Its estimated PMS window can show whether your symptoms cluster in the days before your period, which is useful context before you decide whether a supplement trial makes sense.

For more detail, see vitex (chasteberry) for PMS, vitex (chasteberry) for PMDD, and vitex and mood.

There's no single agreed dose. The 2005 review in American Family Physician noted that standardization and dosing recommendations for chasteberry were still unresolved, and that hasn't changed much since.

Trials have used different extracts, strengths, and schedules, including the proprietary extract BNO 1095 used in several breast-tenderness studies. Most products are taken once daily, often in the morning, but the strength per dose varies by brand, so the amount on one product's label isn't interchangeable with another's.

Because of that variation, check the label of the specific product you're considering rather than assuming a standard dose exists. If you're already on other medication, ask a pharmacist about the amount before you start. For a closer look at doses used in research and on common labels, see vitex dosage.

Vitex is generally well tolerated. The most commonly reported side effects are mild: nausea or other stomach upset, headache, dizziness, and dry mouth. These usually don't require stopping the supplement, though you should stop taking it if any of them are severe or don't settle.

Mood-related side effects are rarer, but worth knowing about. One case report described a person who developed psychotic symptoms after starting vitex for PMS, which resolved after stopping it (Archives of Clinical Psychiatry, 2019). A single case report can't tell you how often this happens, or prove vitex caused it, but it's a reason to stop taking vitex if you notice confusion, unusual thoughts, or a mood shift that feels different from your usual premenstrual pattern.

For a fuller list of reported side effects, see vitex side effects and vitex and mood.

The main interaction to know about involves dopamine. Because vitex's main effect runs through dopamine receptors, the American Family Physician review advises caution if you're taking a dopamine agonist or antagonist, which includes some Parkinson's disease medications and some antipsychotics.

No other herb-drug interactions were reported in that review, but that reflects limited research, not proof of safety alongside everything. If you're on hormonal birth control, an SSRI, or any other daily medication, treat that as a reason to ask a pharmacist before adding vitex, rather than a reason to avoid it outright.

A doctor can also help you weigh a supplement against other options, like an SSRI used only in the days before your period or a change in hormonal contraception, depending on your specific pattern of symptoms.