Rosemary does not appear to increase estrogen. The bulk of available research points in the opposite direction: rosemary and its active compounds tend to reduce estrogen activity in the body through several different mechanisms, including blocking the enzyme that produces estrogen and speeding up the rate at which the liver breaks estrogen down.
That said, the picture is more nuanced than a simple yes or no. One animal study did find a rise in estradiol levels tied to a specific rosemary compound, and the explanation may involve the same enzyme rosemary is otherwise known to inhibit. Here’s what the research actually shows.
How Rosemary Affects Estrogen Production
Estrogen is made from androgens by an enzyme called aromatase, sometimes referred to as estrogen synthase. It’s the only enzyme in the body that performs this conversion. Several compounds naturally present in rosemary have been shown to interfere with aromatase activity, which means they can reduce the amount of estrogen your body produces.
Ursolic acid, one of rosemary’s phytocomponents, has a molecular shape similar to androstenedione, the androgen that aromatase normally converts into estrogen. Because of that resemblance, ursolic acid can fit into the enzyme’s active site and block the normal conversion process. Lab studies show dose-dependent inhibition, meaning the more ursolic acid present, the more aromatase activity drops.
Kaempferol, a flavonoid also found in rosemary, works similarly. In human ovarian cells, kaempferol at moderate concentrations inhibited aromatase by about 30%, and at higher concentrations that figure rose to 50%. The practical result was a significant reduction in estradiol (the most potent form of estrogen) being produced by those cells.
The One Study That Found Higher Estrogen
A study in ovariectomized rats (animals whose ovaries had been removed, eliminating their main estrogen source) found that rosmarinic acid, another key compound in rosemary, was associated with increased serum estradiol levels. The researchers proposed that rosmarinic acid or its breakdown products might actually boost aromatase activity in tissues outside the ovaries, such as fat tissue and bone, where small amounts of estrogen can still be produced by converting circulating androgens.
This finding seems to contradict the aromatase-inhibiting effects of rosemary’s other compounds. The most likely explanation is that different compounds within rosemary push estrogen metabolism in different directions. Rosmarinic acid may enhance aromatase in some tissues, while ursolic acid and kaempferol suppress it. Which effect dominates likely depends on the form of rosemary consumed, the dose, and the individual’s hormonal baseline. It’s worth noting this was an animal study in a very specific hormonal context (no ovaries), so it may not reflect what happens in someone with normal ovarian function.
Rosemary May Speed Up Estrogen Breakdown
Beyond production, rosemary also appears to affect how quickly estrogen is cleared from the body. There is evidence, though considered preliminary, that rosemary enhances the liver’s rate of deactivating estrogen. This is a separate mechanism from aromatase inhibition. Even if estrogen levels were temporarily raised by one pathway, faster liver clearance could offset that effect.
This liver-related activity is why some references flag rosemary as a possible concern for people taking estrogen-containing medications, including hormonal birth control or hormone replacement therapy. If rosemary accelerates estrogen breakdown in the liver, it could theoretically reduce the effectiveness of those medications.
Rosemary’s Effects on Estrogen Receptors
There’s a third layer to this story. Even when estrogen is circulating in the blood, it only works by binding to estrogen receptors on cells. Research on breast cancer cells found that rosemary extract substantially reduced the expression of the estrogen receptor protein (known as ESR1). With fewer receptors available, estrogen has fewer docking points and less ability to stimulate cell growth, even if blood levels remain unchanged.
In lab studies on breast cancer cell lines, this receptor reduction led to cell cycle arrest and apoptosis (programmed cell death). One of rosemary’s compounds, carnosic acid, was also shown to enhance the effects of tamoxifen, a drug that blocks estrogen receptors in breast tissue. The combination produced significantly greater inhibition of cancer cell growth than either substance alone.
What This Means in Practical Terms
If you’re wondering whether adding rosemary to your diet will raise your estrogen levels, the overall weight of evidence suggests it won’t. The dominant effects of rosemary’s compounds point toward less estrogen activity: reduced production through aromatase inhibition, faster clearance through the liver, and fewer active receptors on cells. The single finding of increased estradiol came from one specific compound in surgically altered animals and doesn’t override the broader pattern.
That said, a few practical points are worth knowing. If you take estrogen-based medications, regular consumption of concentrated rosemary extract (not just occasional cooking use) could potentially interfere with how those medications work by speeding up estrogen metabolism. And if you’re managing an estrogen-sensitive condition like certain types of breast cancer, the research on rosemary’s interaction with treatments like tamoxifen is still limited to lab and animal studies. The culinary amounts of rosemary used in cooking are unlikely to produce meaningful hormonal shifts in either direction. Concentrated supplements are where the effects become more relevant, and more uncertain.