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Historically, progesterone (eg Natpro) and synthetic progestins have been lumped together with respect to their safety profiles, although they are very different in their molecular structure and effects.[This is discussed in the section on Bioidentical (Natural) Progesterone vs Synthetic Progestins.]

There is no documented evidence in the scientific literature of any cases of cancer as a result of treatment with bioidentical progesterone. Unfortunately, progesterone has been implicated in the development of breast cancer because of the results of large trials in which an increase in the incidence of breast cancer was seen when synthetic progestins were used in combination with estrogens for postmenopausal hormone therapy. These studies, such as the Women’s Health Initiative, DID NOT use bioidentical progesterone.

A large European study, on the other hand, found that women using bioidentical progesterone plus estrogen had a lower risk of breast cancer than women using estrogen alone, whereas women using synthetic progestins plus estrogen had a significantly higher risk of breast cancer. [See the section on Progesterone and Breast Health for the research on progesterone and breast cancer.]

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Progesterone side effects

No adverse progesterone side effects have been documented to date.

Many women mistakenly believe the reaction they get when first starting progesterone therapy is due to progesterone. This is not the case. The 'adverse' side affects are caused by progesterone activating the oestrogen receptors, which in turn causes oestrogen dominance symptoms.

When beginning to use progesterone cream any of the following symptoms might occur...

  • nausea
  • mild depression
  • bruising
  • dizziness
  • headaches/migraines
  • aches and pains
  • hot flushes
  • bloating/weight gain due to water retention
  • constipation
  • tiredness/sleeping problems
  • breast tenderness
  • spotting
  • a period which comes either earlier or later than usual
  • a period which is heavier or longer than normal
  • skin problems
  • hypoglycaemia

If you have a naturally high level of oestrogen or have been on HRT (hormone replacement therapy) or the contraceptive Pill for any length of time, then progesterone will make you more sensitive to the oestrogen in your body.

This is caused by progesterone activating the oestrogen receptors, which in turn causes the oestrogen dominance symptoms above.

Some women experience these perceived progesterone side effects, others not at all, men never do!

If any of these symptoms do occur, then either increase the dose and persevere until the symptoms disappear, or reduce the dose considerably to begin with and then gradually increase it over a month or two.

The Pill and HRT contain oestrogen and synthetic progesterone (which is commonly called progestin). Progestins cause natural progesterone levels to drop, leading to many of the above symptoms.

Progesterone has been safely used up to dosages of 2,400mg/day (ref. Dr Dalton, London). A dose as high as this is needed to reverse post natal psychosis, anything less will not achieve the desired result.

All the successful studies done on progesterone use between 100mg to 200mg per day. This equates to 3ml to 6ml of Natpro per day. Some go as high as 400-600mg/day, one as high as 1200mg/day as it was the oral variety.

Progesterone side effects references

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