It is important that progesterone levels are kept stable in order to maintain good health. In women, these levels can vary, but rarely in men. Because progesterone levels start to drop after 12/13 hours, it is so important to use progesterone cream no less than twice a day to prevent the levels from spiking.

Progesterone is very important and plays a major role in the body.  Progesterone:

  • is not exclusively a female hormone 
  • is not a sex hormone as so many are led to believe, it plays no part in the secondary sexual characteristics which develop at puberty
  • is the precursor to the two sex hormones estrogen and testosterone
  • is secreted primarily by the ovaries in females and the testes in men. The brain, glial cells and adrenal glads produce smaller amounts
  • there is no difference between men and women other than the luteal phase.  There are no great quantitative differences between men and women, at least outside the luteal phase

Progesterone levels rise sharply during the luteal phase of the monthly cycle, more than the follicular phase. Levels rise from less than 1ng/L to 20-40ng/mL. Saliva levels are higher, please read The Paradox ZRT Labs.


Progesterone levels should always be tested when progesterone peaks at mid-luteal phase which occurs approximately 7 days after ovulation or before bleeding in ALL women. Low levels are found for the rest of the month, or it rises in the early luteal or falling in the late luteal. Therefore it is pointless testing levels any other time.


It makes no difference when men have their levels tested. 

There are two things that are important when testing progesterone levels:

  • the unit measured - SI or conventional. They cannot be compared, a conversion is needed
  • blood (serum) or saliva test. These cannot be compared

Often women who supplement with a progesterone cream are told that their levels are far too high which causes concern for some women. However, there is no need for concern, the main concern is whether or not all adverse symptoms of excess estrogen have cleared. If there are no adverse symptoms, then the amount of progesterone cream can be reduced slowly until you reach an amount that suits you. Please read How to use Progesterone Cream.

 Fluctuating progesterone levels, coupled with the rise and fall of estrogen levels cause:

  • mood changes
  • change in sleep patterns
  • cravings/appetite
  • PMS
  • etc etc

The ratio between progesterone and estrogen is vital, if they fluctuate, problems arise. If there is too much estrogen in relation to progesterone then all hell can break loose. The ratio between progesterone:estrogen (E2) should be around 600:1.

The range given by most labs is 10-100 progesterone to 1 oestrogen. But to feel really well the ratio should be 600:1 and over.  Please read the Hormone Testing page.

Estrogen being an excitatory hormone, causes cells to divide and multiply, including fat cells. Excess estrogen is implicated in:

Please read the Estrogen Dominance, HRT and Contraceptive pages for more information.

Progesterone is a calming, anti-inflammatory hormone which reverses the above symptoms.

Sadly there are well over 100 Estrogen mimics in our Environment today. They are in our food, air, water, plastics, skin care products especially sunscreens to name but a few. They all affect our health and how we feel, men included. For more information please read Our Stolen Future and Skin Deep.

It is so important to make sure that the balance between progesterone and estrogen is correct.

Please read this important page - Saliva Hormone Testing by Dr David Zava.


See details on complete Hormone Testing.



Many are confused when it comes to saliva testing as progesterone delivered transdermally causes a dramatic increase in salivary hormones and not with serum levels. For example, 30mg of progesterone cream results in an average rise in salivary levels from about 50pg/ml (0.05ng/ml) to 500-3000pg/ml (0.5 - 3ng/ml, a 10-60 fold increase. This increase is even greater when 100-200mg is used per day. This results in salivary progesterone levels to rise as high as 10,000-100,000pg/ml (10-100ng/ml). Whereas serum progesterone levels only increase by about 4 fold, from about 0.5 to 2-3ng/ml. The same disproportionate increase in salivary hormone levels is seen with the use of transdermal delivery of all the other hormones i.e. estradiol, testosterone, DHEA etc. See ZRT Saliva test kits.

Depending on how severe symptoms are, women should use between 100-200mg per day, more if symptoms are extreme. Men should use between 10-100mg per day. Please read How to use Progesterone Cream for more information.

Please read the following pages:

Estrogen Dominance

How to convert Conventional untis into SI units

This is a good website for converting SI Units for Clinical Data.

"All systems of weights and measures, metric and non-metric, are linked through a network of international agreements supporting the International System of Units. The International System is called the SI, using the first two initials of its French name Systme International d'Units. The key agreement is the Treaty of the Meter (Convention du Mtre), signed in Paris on May 20, 1875. 48 nations have now signed this treaty, including all the major industrialized countries. The United States is a charter member of this metric club, having signed the original document back in 1875."

The Conversion

  • to convert from the conventional unit to the SI unit, multiply by the conversion factor
  • to convert from the SI unit to the conventional unit, divide by the conversion factor


Component Conventional       Unit Conversion Factor SI Unit
Progesterone ng/mL 3.8 nmol/L
Estradiol pg/mL 3.671 pmol/L
Estriol ng/mL 3.467 nmol/L
Estrone ng/dL 37 pmol/L
Testosterone ng/dL 0.0347 nmol/L