During a woman’s reproductive years, her hormones go through a regular cycle each month. During the luteal phase of her cycle, her oestrogen levels climb progressively over the two weeks leading up to her period. Normally, the body will produce enough progesterone to balance this oestrogen build up. In some women, the oestrogen production is excessive during these two weeks or the progesterone production is insufficient. This imbalance of a high oestrogen to progesterone ratio is the most common cause of hormonal headaches in women. Sometimes this can be quite an extreme headache, even progressing to a migraine.

But headaches can occur at other times in a woman’s cycle as well. The cause of a hormonal headache is dependent on which part in a women’s monthly cycle it occurs. Mid cycle headaches are usually caused by the mid cycle oestrogen surge and subside within a couple of days. Headaches pre-menstruation or during menstruation are related to the oestrogen drop off that occurs pre-bleed or during the bleed.

A study done by the internal medicine department of the University of Cincinnati, Ohio showed the risk of having up to 10 headaches in a month increases by 50% as oestrogen levels drop and women enter menopause. The concept of "estrogen withdrawal" in which declining estrogen levels trigger headaches is well known for menstrual periods. But there have been suggestions that the concept of estrogen withdrawal can extend much longer than just the 5 to 7 days; it can extend for years in some women. Hence one of the most common symptoms during menopause along with hot flushes is headaches.

As this phase is quite dynamic, women that fill up a symptoms calendar to track their headaches are able to achieve better success in their treatment. The symptoms calendar helps identify when in the cycle the headaches occur and their duration. This in turn can be used to deliver the appropriate treatment for the right amount of time. The symptoms calendar also helps the patient monitor their progress through the program.

Another consideration is that hormone receptors and their sensitivity also have a role to play in onset of the headaches. Hence it is important to use the right type of HRT preparation. Studies suggest that conjugated estrogens probably worsen headaches in most women. The biochemical structure of the hormones used in BHRT – the oestrogen and progesterone – all have a biochemical structure that is identical to what the patient is producing herself. This is distinct from most synthetic HRT products like Premarin and Provera, that have a chemical structure considerably different to what the body produces naturally. BHRT is compounded on a patient-by- patient basis. This allows for the correct combination of hormones for each individual. This is different to the commercial products where it is a one size fits all treatment. Thus ensuring patients on BHRT get the best possible outcome.