Making Sense of HRT: Bioidentical Hormones vs HRT

Open palm containing several pillsHormone replacement therapy (HRT) can be confusing enough, but it sometimes gets even more so when you’re faced with an array of different products — bioidentical estrogen, equine estrogen, progestin, bioidentical progesterone gel, patches, pills, all with different claims, and positives and negatives.

Probably one of the more confusing aspects of HRT is when people talk about synthetic versus bioidentical HRT.

You’ve heard the terms being used — but what do they really mean? What’s bioidentical and what’s synthetic? And what are the differences?

It can seem complicated, without a doubt, but we’ll do our best to clarify things. In this helpsheet you’ll find an examination of this issue to help you better understand and take charge of your healthcare.

What are Synthetic Forms of HRT?

This is the type of HRT that has been most widely prescribed for years — estrogens like Premarin and progestins like Provera, as well as low-dose birth control pills.

Synthetics refer to man-made hormones, as you’d expect — hormones that are made from chemical sources that approximate the hormones the human body makes. But it also refers to Premarin (and its offshoots) which, although made from a natural source (horse urine), aren’t the same as your endogenous estrogens (i.e. those made within your body).

Upset dark haired woman

In fact, some synthetic estrogens (such as ethinyl estradiol, found in many birth control pills, and the equine estrogens in both Cenestin and Premarin) are stronger than human estrogens.

Supporters of bioidentical hormones have made claims that synthetic HRT may cause your liver to work harder in comparison to the use of bioidentical HRT. However, this claim (like many others) is unproven.

On the plus side, synthetic conjugated estrogens (as in Premarin) are the most widely studied form of estrogen — so there has been much more research on its effects in the human body. It’s been shown to eliminate menopause symptoms and help prevent bone loss. In addition, it may help protect against cardiovascular disease, the risk of which is elevated in women with early menopause (1).


For some time the only easily available choice for progesterone replacement was progestin — synthetic progesterone. Progestin isn’t exactly like progesterone, but has many of the same attributes and opposes estrogen in your body like natural progesterone.

Synthetic HRT has been widely studied, for example in the Women’s Health Initiative (WHI) and The Million Woman Study. The extent to which these study findings apply to bioidentical hormones has been debated but you should assume the same side effects apply to bioidentical hormones because no evidence exists to prove otherwise. In effect, then, you should not automatically assume that synthetic means badand bioidentical means good.

What are bioidentical Forms of HRT?

Prescription pills spilling from bottleIn most discussions of HRT, “bioidentical” refers to estrogens and progesterone that are often man-made, but from natural plant sources. Most of them are naturally occurring and in theory, bioidentical to the hormones your body makes.

In other words, they don’t approximate your hormones but mimic them exactly. Supporters argue that, because they are the same as endogenous hormones, our bodies ought to be better equipped to work with them.

The problem with all of these claims is that they simply haven’t been verified by high quality evidence.

An advocate named Suzanne Somers (who appeared on the Oprah Show) has been one of the most vocal supporters of bioidentical hormones, although she’s also received criticism for making unsubstantiated claims regarding their benefits relative to synthetic HRT.

The argument, typically, is that we can more easily metabolize them and break them down so our livers and kidneys can excrete them more efficiently. Given this, they may not accumulate in the body to the same extent, causing fewer side effects. Again, these claims are unproven.

As with synthetic estrogen, bioidentical estrogens help to eliminate the symptoms of menopause, prevent bone loss and may help protect against cardiovascular disease. However, its unclear whether or not they cause fewer side effects than synthetic estrogen.

Okay, seems pretty straightforward, right? But there is one recent exception to this clear-cut definition:

Cenestin is a conjugated estrogen. It’s natural in that it’s made from plant sources, but it’s not bioidentical to human estrogens. Instead, as a conjugated estrogen, it’s a plant-derived variant of Premarin. It’s not horse urine, like estrogen, but the estrogens in it are copies of equine estrogens.


Over the past few years, bioidentical prescription progesterone has become available. As with bioidentical estrogen, it’s plant-derived. Similar to the debate regarding estrogen, claims that bioidentical progesterones cause fewer side effects than their synthetic cousins are unproven.

Bioidentical estrogens include: Estrace, Estratab, Ogen, the estradiol patches such as Climara, Alora, Vivelle, Estraderm, Esclim, FemPatch, etc, and Tri-Est

Bioidentical progesterones include: Prometrium and Crinone

What about Phytoestrogens? Aren’t they considered bioidentical HRT?

Some people do call phytoestrogens — like soy isoflavones and flax seed — bioidentical HRT, but this is not strictly accurate. Generally these substances are considered only as a substitute to HRT and sometimes preferred by women with mild symptoms. HRT, in contrast, refers to prescribed hormones to address symptoms resulting from changes in your hormone levels.

Glass of soy milk with soybeans

That said, for some women, phytoestrogens can have an important role to play in managing early menopause. They may help to minimize certain common symptoms.

Some women taking HRT also opt to take phytoestrogens in addition. Meanwhile, women not on HRT often use them to tackle symptoms — even though they’re much less potent than prescription estrogen. At the most, they’re only about 2 percent of the strength of estradiol — the primary human estrogen. Nevertheless they produce an estrogenic reaction in your body.

For more information on phytoestrogens read our helpsheet: What Does The Science Say About Natural Remedies?.

Studies have shown potential benefits that include help with symptoms like hot flashes and night sweats. Remember though, always consult your doctor before beginning a new regimen or changing your existing regimen.

Phytoestrogens include: Lignans (found in sources including cereals and vegetables, especially high in flaxseed); Isoflavones (found in legumes, especially high in soy); Coumestans (found in red clover and alfalfa sprouts. A potent phytoestrogen, although still about 200 times weaker than human estrogen).

Bioidentical Versus Synthetic: What’s Best for You?

It’s important to remember that the hype surrounding bioidentical hormones hasn’t been substantiated by high quality studies.

Young dark haired woman screaming with hands on head


The stated position of reputable organizations such as The Endocrine Society and ACOG is that no credible evidence exists to suggest bioidentical hormones are either more effective or more safe than conventional forms of HRT.

After the WHI study findings, the FDA began requiring the packaging of both synthetic and bioidentical forms of HRT to carry a so-called ‘black box‘ warning. 

HRT from compounding pharmacies doesn’t carry this warning, however, this doesn’t imply that it’s safer (only that it isn’t FDA approved).

Ultimately, there’s no definitive way to provide a blanket answer to each and every woman. It’s one of those cases where it’s up to you to decide in conjunction with your doctor.

While some individuals have claimed that bioidentical forms of estrogen are a better choice, they can also be more costly and carry no proof of added benefits. Furthermore, many doctors feel more comfortable prescribing Premarin because it has been studied more extensively.

Opinions in this area are notoriously contentious and those who’ve come out in support of bioidentical hormones have been rightly refuted by experts (2, 3, 4, 5).

It’s crucial to work alongside your doctor to determine what is right for you. There are many ethical, political and practical opinions floating around about HRT and its different forms. This can often feel like a distraction in the pursuit of effective treatment.

Woman pointing to pill packet in jeans

As we’ve seen, the bioidentical vs synthetic debate is heated and highly polarized. Nevertheless, there is no scientific proof for most of the claims made in support of bioidentical HRT. Ultimately, your best course of action is to find a doctor you can work with and trust.  Don’t be afraid to try different forms of HRT until you find the one that works best for you. And remember: there’s no “one-size-fits-all” solution when it comes to HRT. The aim should be to find something that best addresses your particular needs and symptoms.

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