Common causes for reduced testosterone production includes:

• diseased or compromised organs that produce testosterone (ovaries, brain, adrenals)
• removal of both ovaries (bilateral oophorectomy) or premature ovarian failure which may cause an immediate 50% reduction in testosterone levels
• removal of adrenal glands (adrenalectomy) which may also cause an immediate 50% reduction in testosterone levels
• pituitary gland in the brain is affected by disease (hypopituitarism) which may cause a 100% reduction in testosterone levels

Causes for poor testosterone availability due to increased Sex Hormone Binding Globulin (SHBG)

SHBG is a transporter protein in the blood that moves hormones around the body. While SHBG has an important role to play in the body, SHBG may tend to attach and thereby "lock" as much as 99% of the body's testosterone, thus rendering the hormone inactive. Because of this, the body is only able to utilize the remaining unattached testosterone.

In order to establish an accurate determination of how much testosterone is bio-available, pathology labs need to measure the Free Androgen Index (FAI) which is calculated by the total testosterone level in the blood divided by the SHBG level multiplied by 100.

Factors which can increase SHBG concentration include:

• Oral estrogens (including oral contraceptives, HRT tablets)
• Thyroxine tablets
• Increasing age
• Alcohol
• Smoking
• Some anticonvulsants e.g. phenytoin
• Pregnancy
• Reduced liver function

Taking oral estrogens increases SHBG concentration and reduces available testosterone. However, women undergoing standard estrogen patch therapy or estrogen gels and creams do not experience these problems.

Women who experience lowered sexual drive or unexplained lethargy and fatigue as a result of hormone therapy or the Pill are advised to change to a non-oral dose to reduce the SHBG levels which will free up testosterone.

Non-Hormonal drug therapies that may induce symptoms that mimic testosterone deficiency

Even if women have sufficient testosterone production and lower SHBG concentration, certain kinds of medication may result in symptoms that mimic testosterone deficiency. Medications which may interfere with sexual desire include:

Medication	Use
SSRI's, tricyclics	Depression
Oral oestrogens	Oral contraceptive pill, HRT
Medroxyprogesterone	Contraceptive, HRT
Clonidine	Hot flushes
Medroxyprogesterone	Contraceptive, HRT
Spironolactone, Androcur	Hirsutism
Danazol	Endometriosis
Benzodiazepines	Anxiety, insomnia
Beta blockers	Hypertension
H2 antagonists	Oesophageal reflux
Ketoconazole	Vuvlo-vaginal candidiasis
Gemfibrazol	Hyperlipidaemia

Under no circumstances should patients change or cease taking medications without the consent of their doctor. If a patient is taking one or more of these medications and experiencing a lowered sexual desire he or she should consult their medical practitioner.

Recommended next page - Treatment of Testosterone Deficiency in Women