Synthetic and natural hormones: what’s the difference?

When considering HRT, it’s important to know what might be best suited to you

If you decide to take HRT, you will usually be given one or more of these hormones: oestrogen, progesterone, and testosterone. Before starting HRT, ensure it’s natural rather than synthetic, if possible. Having the right dose and type of HRT is important to improve symptoms as well as to improve future health.

HRT containing natural (body-identical) hormones – oestrogen, progesterone, and testosterone – matches those hormones produced by your body. Body-identical HRT includes oestrogen delivered via patches, gels, or sprays, micronised progesterone and testosterone as a gel or cream. They are safer and not usually associated with risks.

These hormones are derived from yams and soy, and are the same chemical structure as natural hormones.

RELATED: Body identical hormones

Natural oestrogen

All types of transdermal oestrogen, which is oestrogen delivered directly through the skin (as a patch, gel or spray), contain natural (body-identical) oestrogen.

There are some oral oestrogen tablets that are body identical such as Elleste Solo and Zumenon. These contain the hormone oestradiol, which is identical to the oestrogen made naturally in your ovaries. While there remains a small increased risk of blood clot with any oral oestrogen preparation, it is less with the body identical tablets [1].

Synthetic oestrogen

Early hormone treatments included oestrogen derived from pregnant horse urine, which contained various hormones. There are also other types of tablet oestrogen that are man-made and their chemical structure is different to that of oestradiol, which is the beneficial type of hormone produced before menopause.

Synthetic hormones differ chemically from those produced naturally by the body, leading to distinct metabolic effects and risks, such as blood clots and some cancers. These older types of synthetic oestrogen blends are still readily available – while their use is reducing, some women do continue to have them prescribed, particularly those who have been taking HRT for a number of years.

Natural progesterone

If you still have your uterus (womb), taking oestrogen can cause the lining (endometrium) to thicken. To prevent this thickening, you will be required to take progesterone. Progesterone can still be beneficial to women who have had a hysterectomy as it works all over your body.

Like natural oestrogen, natural (body-identical) progesterone in HRT is derived from yam plants or soy and has the same chemical structure as the progesterone your body produces.

Progesterone is hard to absorb through the skin and gut – by micronising it (reducing the particles to a very fine powder and suspending in an oil) and putting it in capsule form it is easily absorbed either by swallowing it or inserting vaginally. Utrogestan and Cyclogest are common brand names of natural progesterone.

Natural progesterone has fewer side effects than synthetic alternatives and is not associated with any risks to your health – it does not increase the risk of blood clots or heart disease and helps to lower blood pressure and cholesterol.

Synthetic progestogens

Sometimes, synthetic versions of progesterone are used, which are called progestogens, or progestins. Progestogen is a molecule, either natural or synthetic, which has similar effects to progesterone and binds to the progesterone receptor. Progestins are synthetic compounds, they are made in a laboratory, which mimic the action of progesterone. These have a slightly different chemical structure to natural progesterone.

Synthetic progestins and progestogens have been found to have a small risk of blood clot, heart disease and breast cancer. These risks are very small, and your actual risk depends much more on your overall health, genetics, weight, and lifestyle habits.

While the Mirena (and Levosert) coil is a synthetic progesterone, it is a much lower dose and usually just works locally on the lining of the womb.

RELATED: Progesterone intolerance

What about combined patches and pills?

Combined HRT is oestrogen and progesterone and is available in patches and tablets.

Patches contain natural (body identical) oestrogen but the progestogen part is synthetic.

Many combination tablets contain natural oestrogen but the progestogen is synthetic. One tablet, branded in the UK as Bijuve, contains both natural oestrogen (oestradiol) and progesterone.

Testosterone

Testogel and Tostran gels and AndroFeme cream are all body identical and are derived from the yam plant or soy. AndroFeme contains almond oil so should be avoided if you have an almond allergy.

What should I choose?

Your healthcare provider will help you choose the right form of HRT, weighing up benefits and risks, but for most women it is preferable to choose natural (body-identical) hormones.

When reading headlines or studies about HRT, check the type included – many studies include older types of HRT so their findings are not always relevant to the majority of women.

RELATED: How to talk to your doctor about HRT and get results

References

1. Vinogradova, Y. et al. (2019), ‘Use of hormone replacement therapy and risk of venous thromboembolism: nested case-control studies using the QResearch and CPRD databases’, British Medical Journal, 364 k4810. doi:10.1136/bmj.k4810