Written by Dr Phoebe Howells, reviewed by Dr Katherine Joseph. 

Phoebe, a doctor since 2012, has a decade of experience in Obstetrics and Gynaecology, with a focus on fertility. Her dedication led to a clinical fellowship in Reproductive Medicine at a top London fertility clinic. She's authored articles, shared insights at global conferences, and contributed to fertility trials for women with adenomyosis. Phoebe's all about crafting tailored, evidence-based care and achieving the best results for people navigating fertility challenges. While working in London, she enjoys the countryside life in Kent.

Why has PCOS changed to PMOS?

For many years, Polycystic Ovary Syndrome (PCOS) was one of the most commonly diagnosed hormonal conditions affecting women of reproductive age. However, experts have long recognised that the name didn’t accurately reflect the condition. Not everyone diagnosed with PCOS has polycystic ovaries, and the condition extends far beyond reproductive health. 

In 2026, following international consensus, the condition was renamed Polyendocrine Metabolic Ovarian Syndrome (PMOS). The new name better reflects the complex interplay between hormones, metabolism and ovarian function that characterises the condition. This international consensus was published in The Lancet, a highly respected journal, in May.  

If you’ve recently heard the term PMOS or are wondering whether it changes anything about diagnosis or treatment, this guide explains what the new terminology means, how PMOS affects fertility and hormone balance, and why myo-inositol has become one of the most researched supplements for supporting people living with the condition.

 

What is PMOS?

Polyendocrine Metabolic Ovarian Syndrome (PMOS) is a lifelong endocrine and metabolic condition affecting approximately 8-13% of women of reproductive age worldwide. 

It involves a combination of hormonal imbalances, disrupted ovulation, insulin resistance in many individuals, increased androgen production (male hormones also found in females), metabolic dysfunction, and ovarian changes. 

The former name, polycystic ovary syndrome (PCOS), emphasised just one potential feature of the condition: the presence of polycystic ovaries. However, many individuals diagnosed with PMOS do not have polycystic ovaries, while some people with polycystic-appearing ovaries experience no symptoms at all. Furthermore, these structures are not true ovarian cysts. Rather, they are multiple normal follicles, which are fluid-filled sacs within the ovaries that each contain an immature egg. During each menstrual cycle, these follicles develop and move toward the ovarian surface, where one is typically selected to mature and release an egg during ovulation. However, in those with PMOS, several follicles begin developing each cycle but stall before one is selected for ovulation, so they accumulate rather than resolve, creating the polycystic appearance. 

The new name recognises that PMOS is primarily an endocrine and metabolic disorder, rather than simply an ovarian condition.

 

Why the terminology changed from PCOS to PMOS

Medical terminology should accurately describe disease processes. Experts increasingly felt that the name Polycystic Ovary Syndrome caused confusion because it suggested that ovarian cysts were essential for diagnosis and also overlooked the significant metabolic complications. 

The new term Polyendocrine Metabolic Ovarian Syndrome better reflects the fact that multiple hormone systems are involved, alongside metabolic changes such as insulin resistance and altered glucose metabolism.

Importantly, the diagnostic criteria themselves remain largely unchanged during the transition. The name has evolved to improve understanding rather than redefine the condition.

 

How does PMOS affect fertility?

One of the most common challenges associated with PMOS is difficulty conceiving. Normal fertility depends on regular ovulation. In PMOS, hormonal imbalances can disrupt this process, preventing eggs from developing and being released consistently. One way to think about this is that the large number of follicles in the ovaries may create mixed hormonal signals, making it more difficult for a single follicle to respond and become dominant. As a result, ovulation may be delayed or fail to occur, leading to irregular menstrual cycles.

Common reproductive effects include irregular menstrual cycles, infrequent ovulation, sometimes absence of ovulation and reduced egg quality in some individuals. 

Not everyone with PMOS experiences infertility. Many conceive spontaneously, while others may benefit from lifestyle interventions, ovulation induction medication or assisted reproductive technologies. For example, research consistently shows that improving metabolic health can also improve reproductive outcomes.

 

Hormone imbalance in PMOS

PMOS affects several hormone systems simultaneously.

Androgens

Many individuals produce higher-than-normal levels of testosterone and other androgens.

This may contribute to acne, unwanted facial or body hair (we use the term hirsutism), scalp hair thinning, and disrupted ovulation. 

Insulin

Around 50-70% of people with PMOS have some degree of insulin resistance. When the body becomes less responsive to insulin, the pancreas compensates by producing more. High insulin levels stimulate the ovaries to produce additional testosterone, creating a cycle that further disrupts ovulation.

LH and FSH

PMOS may also alter communication between the brain and ovaries by changing levels of luteinising hormone (LH) and follicle-stimulating hormone (FSH). This imbalance contributes to incomplete follicle development and irregular ovulation.

 

Understanding PMOS phenotypes

Not everyone experiences PMOS in the same way. Clinicians recognise several phenotypes, meaning different combinations of symptoms. Understanding an individual’s phenotype helps clinicians tailor treatment according to their symptoms and goals.

Phenotype A (Classic PMOS)

• Hyperandrogenism

• Ovulatory dysfunction

• Polycystic ovarian morphology

• Often associated with greater insulin resistance and metabolic complications.

Phenotype B

• Hyperandrogenism

• Ovulatory dysfunction

• Normal ovarian appearance

• Symptoms are often similar to classic PMOS.

Phenotype C

• Hyperandrogenism

• Polycystic ovarian morphology

• Regular ovulation

• Individuals may have fewer fertility concerns but still experience androgen-related symptoms.

Phenotype D

• Ovulatory dysfunction

• Polycystic ovarian morphology

• Normal androgen levels

• Sometimes called “non-hyperandrogenic” PMOS.

 

What is Inositol?

Inositol works by improving how your body handles insulin. Inositol is a group of nine related sugars, all built from the same building blocks, but folded into different shapes. Of these nine forms, two matter in PMOS and fertility conversations: Myo-Inositol and D-chiro-inositol, or a blend of both. Myo-Inositol is the most common form associated with insulin signalling, and D-Chiro-Inositol is more involved in androgen and testosterone regulation. In your blood plasma these usually sit at a Myo-Inositol: D-Chiro-Inositol ratio of 40:1, with this ratio being a key part of research conversations. 

Myo-Inositol

Myo-Inositol is a naturally occurring carbohydrate-like compound that is often referred to as vitamin B8, although it is not officially classified as a vitamin. It plays an essential role in insulin signalling, cell communication, egg maturation, ovarian function and hormone regulation.

The body produces Myo-Inositol naturally, and it is also found in foods including:

• citrus fruits

• beans

• wholegrains

• nuts

• seeds

• cantaloupe

• legumes.

Although dietary intake contributes, the therapeutic doses used in research are considerably higher than those typically obtainable from food alone.

D-Chiro-Inositol

Your body makes most of D-Chiro-Inositol from Myo-Inositol, using a specific enzyme. The role of this form of Inositol is to regulate androgen levels produced by the ovaries, though too much D-Chiro-Inositol can actually push this the wrong way and increase androgen levels. This form of Inositol also helps to regulate glucose stores in muscles and the liver. 

 

Should I supplement with Myo-Inositol?

Overall, international guidelines recognise Myo-Inositol as a supplement with a favourable safety profile that may benefit selected individuals with PMOS, while also acknowledging that higher-quality research is needed to determine which patients benefit most, if at all.

As a supplement, Inositol is typically sold in one of two forms (Myo-Inositol and D-Chiro-Inositol) or as a blend of both.

Where Myo-Inositol may be helpful

Insulin resistance 

One of the strongest lines of evidence for taking Myo-Inositol concerns insulin resistance. Studies consistently demonstrate improvements in fasting insulin, HOMA-IR (a measure of insulin resistance), glucose metabolism, and metabolic markers. These improvements may also reduce long-term risks associated with PMOS, including type 2 diabetes. Because insulin resistance plays such a significant role in many people with PMOS, improving insulin signalling addresses one of the underlying mechanisms rather than simply managing symptoms.

Research suggests supplementation may reduce circulating testosterone while improving menstrual regularity. Some women also report improvements in acne and excessive hair growth, although these changes often take several months and vary between individuals. 

Fertility outcomes

Researchers believe Myo-Inositol may improve certain subtypes of PMOS by enhancing the body’s response to insulin. Improved insulin sensitivity reduces circulating insulin levels, which in turn may reduce ovarian androgen production. Potential benefits include more regular ovulation, improved menstrual cycles, improved egg quality, reduced testosterone levels and better glucose metabolism. Therefore, leading to better fertility outcomes. 

Research into Myo-Inositol has grown substantially over the past two decades, but remains limited in the context of reproductive health. Multiple systematic reviews have found that Myo-Inositol can improve ovulation rates, particularly in individuals with insulin resistance. Restoring regular ovulation may increase the likelihood of spontaneous conception. Several studies also suggest Myo-Inositol may improve pregnancy rates by enhancing egg quality and ovarian function. It is increasingly used before assisted reproductive treatments, although evidence is stronger for improving ovulation than live birth outcomes.

It is important to consider what the guidelines recommend here. The 2023 international guideline on PMOS strongly recommends against Inositol (in any form) as a fertility treatment, describing it as experimental, with benefits and risks "too uncertain."

ESHRE's 2025 guidance went further, strongly recommending against Myo-Inositol for women without PMOS going through IVF. Cochrane, which independently grades evidence, rates the evidence linking Myo-Inositol to live birth as very low certainty. That grade rests on two studies and 84 women in total. NICE's fertility guideline, updated in March 2026, doesn't mention it at all.

 

Where Myo-Inositol may be harmful 

Not everyone with PMOS should necessarily be taking Inositol (in any form), and for those who do not have PMOS, research tells us that Inositol may have the potential to cause harm.

One randomised trial has tested Myo-Inositol for its effects on egg maturity in women without PMOS. In that trial,100 women took 4 g per day for three months. The Myo-Inositol group ended up with fewer eggs and fewer mature eggs than the group that didn't.

 

Why Time to Conceive® For Women doesn’t contain Myo-Inositol

If insulin resistance is what's pushing your testosterone up, as it does in the classical, hyper-androgenic type of PMOS, then bringing it back down is doing real work. As mentioned earlier, around 50% - 70% of those with PMOS have some degree of insulin resistance.

If your hormone levels are already where they should be, there's no excess to correct. When researchers examined this by phenotype, women with normal androgen levels showed no meaningful hormonal change after six months of Myo-Inositol, indicating no benefit from taking it. 

Therefore, we don’t include Inositol in Time to Conceive® For Women because it is not suitable for those who do not have PMOS. And for those who do, the evidence isn’t yet clear-cut as to whether it is suitable to take in all cases of PMOS. We need more research in this area, as not everyone with PMOS has insulin resistance, and it’s not clear whether Inositol offers much benefit to people who fall into that category. There’s further potential to harm egg quality, as recent evidence suggests that the Myo-Inositol to D-Chiro-Inositol ratio (typically found as a combination in supplement products) is important. Too much D-Chiro-Inositol relative to Myo-Inositol could actually work against egg quality.

 

Practical guidance on Myo-Inositol

Although doses vary across studies, the most commonly studied regimen is 2 grams of Myo-Inositol twice daily (morning and evening), for a total daily dose of 4 grams.

It can be taken with or without food, although taking it with meals may reduce the likelihood of mild digestive discomfort.

How long before results are seen?

Improvements are rarely immediate. Most clinical studies evaluate outcomes after three to six months, reflecting the time required for ovarian follicles to mature. Therefore, it is important to take it consistently. 

Is Myo-Inositol safe to take?

Myo-Inositol is generally well tolerated. Reported effects are uncommon and usually mild, including nausea, bloating and mild gastrointestinal upset. 

However, supplements should not replace medical assessment. Anyone experiencing irregular periods, infertility or symptoms suggestive of PMOS should consult their GP or specialist before starting supplementation, particularly if they are pregnant, breastfeeding or taking medication for diabetes. As mentioned, your sub-type of PMOS is also important to consider when evaluating whether Myo-Inositol is right for you to take. 

 

Supporting PMOS beyond supplements

While supplements may help, they work best as part of a broader approach. Lifestyle interventions remain the foundation of PMOS management. These include eating a balanced, fibre-rich diet and engaging in regular physical activity. Also, maintaining a healthy body weight where appropriate, prioritising good sleep and minimising stress. People often find that losing enough weight to reach a healthy BMI helps regulate their menstrual cycles. 

For some individuals, healthcare professionals may also recommend medications such as metformin or ovulation induction treatments depending on fertility goals and metabolic health.

 

Key takeaways

• The transition from PCOS to PMOS reflects a better understanding of the condition as a complex endocrine and metabolic disorder rather than simply an ovarian condition. Although the name has changed, early diagnosis, personalised treatment and ongoing support remain central to improving health outcomes.

• Myo-inositol may improve insulin sensitivity, ovulation, and menstrual regularity, particularly in PMOS subtypes with insulin resistance.  However, current guidance does not recommend Myo-Inositol, and it may be harmful for those without insulin resistance. 

• Understanding the hormonal and metabolic nature of PMOS empowers individuals to make informed decisions about their reproductive health and long-term wellbeing. Much more research is still needed on both PMOS and Myo-Inositol to provide appropriate guidance and support.