50. Is PMDD a Histamine Problem? H1 and H2 Blockers Explained

Could histamine be contributing to Premenstrual Dysphoric Disorder (PMDD)?

In this episode of The Histamine Well Podcast, Joanne explores the growing interest in the connection between PMDD, histamine intolerance, mast cell activation, and hormonal fluctuations. As more women report improvements in PMDD symptoms with antihistamines, the question is gaining attention: could histamine be a missing piece of the PMDD puzzle?

Joanne breaks down the science behind the estrogen-histamine feedback loop, explains how histamine interacts with estrogen and progesterone throughout the menstrual cycle, and discusses why some women experience worsening mood symptoms during the luteal phase.

You'll learn about the role of mast cells, neurotransmitters, neuroinflammation, and hormone sensitivity in PMDD, as well as the potential benefits and limitations of H1 and H2 antihistamines. Joanne also shares her clinical observations on histamine-related hormone symptoms and why addressing underlying drivers of histamine excess may be essential for long-term symptom improvement.

In This Episode You'll Learn:

• What PMDD is and how it differs from PMS
• The relationship between histamine and women's hormones
• How estrogen can increase histamine levels
• The role of progesterone in histamine regulation
• Mast cell activation and hormone-related symptoms
• Why histamine may worsen anxiety, irritability, and mood swings
• The science behind H1 and H2 blockers
• Potential risks of long-term antihistamine use
• Histamine's effects on neurotransmitters including serotonin and dopamine
• The connection between PMDD, MCAS, and histamine intolerance
• Why methylation may play a role in PMDD symptoms
• Common root causes of histamine excess, including SIBO, mold exposure, oxalates, and gut dysfunction
• Natural strategies for addressing histamine-related hormone symptoms

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Transcript

0:00

Hi, it's Joanne. Over the past year or two, I've noticed more and more women talking about the connection between histamine and premenstrual dysphoric disorder, PMDD. Some are reporting significant improvements in their symptoms from antihistamines, particularly H1 and H2 blockers, while others are wondering whether histamine could be the missing piece in a condition that has often been difficult to treat The challenge is that while the stories are compelling, the research is still emerging. We don't yet have large clinical trials showing that antihistamines are an effective treatment for PMDD, but what we do have is a growing understanding of the relationship between histamine, hormones, mast cells, neurotransmitters, and inflammation. So in today's episode, we're going to unpack what PMDD actually is, how histamine interacts with estrogen and progesterone, and why some women may experience worsening symptoms during certain phases of their cycle, and whether H1 and H2 blockers deserve a place in the conversation. We'll also discuss where the evidence is strong, where it's limited, and what I see clinically in women dealing with PMDD, histamine issues, and hormonal imbalances. Welcome to the Histamine Well Podcast, designed for practitioners and patients alike. This is your trusted source for insights on histamine intolerance, methylation, gut health, women's hormones, and much more. I'm Joanne Kennedy, your host, naturopath, author, and educator. Passionate about breaking down complex science into clear, accessible knowledge. Whether you're a health professional or navigating your personal wellness journey, the Histamine Well Podcast bridges the gap between cutting-edge research and practical understanding to empower you with the tools to thrive. Hi everyone. Welcome back to The Histamine Well. Today, we're talking about something that has been gaining a lot of traction lately. And that's the idea that histamine plays a role in PMDD and whether H1 and H2 blockers might actually help. I want to be upfront, this is an emerging area. The research is limited, and a lot of what we know right now comes from our understanding of how histamine and hormones interact rather than from clinical trials on antihistamines and PMDD specifically. But the biology is interesting, and there's enough here to take it seriously. So let's break it down properly. What is PMDD and what makes it different from PMS? PMDD is premenstrual dysphoric disorder. It affects an estimated 3 to 8% of menstruating women, though some studies put that figure as high as 10%. It's a severe cyclical mood disorder, and the key distinction between PMDD and regular PMS is functional impairment. PMDD doesn't just make you feel off, it disrupts your ability to work, maintain relationships, and function day-to-day. Symptoms have to follow a specific pattern. They appear in the luteal phase, that's the second half of your cycle after ovulation, and they resolve within a few days of menstruation starting. Diagnosis requires at least five symptoms, and at least one must be a core mood symptom. Severe irritability, anxiety, depression, or extreme mood swings. Physical symptoms include bloating, breast tenderness, headaches, fatigue, joint pain that can accompany the mood symptoms, but they aren't sufficient on their own as a diagnostic tool. The current gold standard treatment are SSRIs, this is from the medical community, and certain hormonal therapies. But a significant number of women don't respond adequately to these, and that's part of why the histamine conversation is worth having. I know this podcast is all about histamine, and a lot of you have been listening to most episodes, so you know what histamine is. But just for those who are not quite sure how it is actually working in the body, I'm just gonna go over that. Most people know histamine as the thing responsible for allergy symptoms, the itching, the sneezing, watery eyes. But histamine does a lot more than that. It functions as a neurotransmitter in the central nervous system, regulating mood, wakefulness, pain perception, and cognition. It also plays a role in gut motility, immune signaling, and the dilation of blood vessels. Histamine works by binding to receptors, and there are four types: H1, so histamine 1, H2, H3, and H4, each found in different tissues and responsible for different effects. The ones most relevant to this conversation are the H1 and H2 receptors. H1 receptors are found throughout the body in smooth muscle, blood vessels, and the brain. When histamine binds here, you get the classic allergy picture: inflammation, itching, hives. And in the brain, it affects mood, anxiety, and sleep. Then we've got the histamine 2 receptors, the H2 receptors. These are concentrated in the stomach lining, where they regulate acid production, but they're also found in immune cells and blood vessels. Blocking H2 receptor reduces both stomach acid secretion and some aspects of immune cell activity. We've also got histamine 3 receptors, which I'll talk about. They are almost exclusively in the brain and regulate the release of other neurotransmitters, including serotonin, dopamine, and norepinephrine. This is relevant because it means histamine dysregulation in the brain doesn't just affect histamine signaling. It can affect the entire neurochemical environment. So I'm gonna also touch on the oestrogen-histamine feedback loop. I've spoken about this a lot in the podcast, so i'll go over this again, as this is the mechanistic core of the whole conversation. oestrogen and histamine have a bidirectional relationship. Each one amplifies the other, and this loop can cause real problems in people who are already prone to histamine excess. So here's how it works. oestrogen stimulates mast cells. Mast cells are immune cells that store histamine and release it when activated. They express oestrogen receptors, specifically oestrogen receptor alpha, which means oestrogen directly signals them to degranulate, releasing histamine into circulation. oestrogen also suppresses the DAO enzyme. DAO stands for diamine oxidase. It's the enzyme primarily responsible for breaking down histamine in the gut. When DAO activity is reduced, histamine from both internal sources and the diet accumulate rather than being cleared. Histamine then stimulates more oestrogen. This closes the loop. Histamine has been shown to stimulate ovarian oestrogen production, so elevated oestrogen drives more histamine release, and that histamine drives more oestrogen. So it's a self-reinforcing cycle. Now we need to talk about progesterone, as progesterone, in contrast, generally stabilizes mast cells and can support DAO activity, helping to break that loop. This is partly why some people find their symptoms are manageable in the follicular phase when progesterone is low, but oestrogen is more stable. And worse in the luteal phase when progesterone rises, but oestrogen is also still elevated and the whole system is more volatile. Timing-wise, histamine levels tend to peak before ovulation, which corresponds with the oestrogen surge, and again in the luteal phase. And this cyclical pattern overlaps directly with when PMDD symptoms are most severe. So what's actually happening in PMDD? What's the neurological picture? To understand why histamine might matter in PMDD, it helps to know what we currently understand about the neurobiology of PMD more broadly. The leading mechanistic explanation for PMDD is not that people with PMDD have abnormal hormone levels. They don't typically. What appears to be different is their sensitivity to normal hormonal fluctuations, particularly around a neuroactive steroid called allopregnanolone. So allopregnanolone is a metabolite of progesterone, and it normally acts as a positive modulator of GABA A receptors. GABA being the brain's primary inhibitory neurotransmitter. In most people, the rise and fall of allopregnanolone across the cycle has a calming, stabilizing effect. In people with PMDD, there appears to be a dysregulated or paradoxical sensitivity to allopregnanolone, where those fluctuations instead trigger anxiety, irritability, and mood instability. This is also why SSRIs can work in PMDD even when taken only during the luteal phase. They affect the allopregnanolone metabolism as well as serotonin. Now, lay histamine on top of this. Histamine in the brain influences serotonin, dopamine, and norepinephrine signaling through H3 receptors. If histamine is elevated in the luteal phase because of oestrogen-driven mast cell activation, it's adding a neuroinflammatory load and disrupting neurotransmitter balance in the brain that's already sensitive to hormonal changes. That's a plausible reason why histamine could amplify PMDD symptoms without being the root cause of them. So now let's talk about these medications, the H1 and H2 blockers. H1 antihistamines are the ones most people are familiar with. They block histamine from binding to H1 receptors, which reduces inflammatory and immune responses, as well as some central nervous system effects. There are two generations of these H1 blockers. The first generation H1 blockers, such as Benadryl being the main one, these cross the blood-brain barrier readily and have significant anticholinergic effects, meaning they block acetylcholine, a neurotransmitter important for memory and cognition. This causes the drowsiness they're known for, but also the cognitive side effects. A 2015 study found that cumulative anticholinergic drug use was associated with a 54% higher risk of dementia. Now, that's for sort of use of three or more years compared to short-term use. More recent research is mixed. A 2023 study found no conclusive link to dementia, but did find a significant association with mild cognitive impairment. Either way, first-generation antihistamines are not appropriate for regular cyclical use in this context. Second-generation H1 blockers, such as fexofenadine and loratadine have a much better profile. They cross the blood-brain barrier minimally, have low anticholinergic activity, and are less sedating. These are the ones being discussed in the context of PMDD. People typically reporting using them five to seven days before expected symptom onset and continuing until menstruation begins. Before we go any further, I want to speak directly to the practitioners and students listening. If you're intrigued by histamine and methylation and eager to expand your knowledge in this fascinating area, we offer the Histamine and Methylation Online Group Coaching course. The only program of its kind. It covers everything you need to know about histamine and methylation, providing both the theory and guidance you need to treat these issues effectively in clinical practice. We cover SIBO, hormonal imbalances, oxalates, MTHFR, the four pathways of methylation, including the folate pathway, methionine pathway, tetrahydrobiopterin pathway, and the all-important transsulfuration pathway, and much more. The program is delivered by detailed online webinars and handouts for you to keep, and for eight weeks you'll meet with me for live coaching calls in a private community space with other practitioners from all over the world dealing with histamine and methylation issues in their patients every day. Together we learn so much. To learn more and apply, visit joannekennedynaturopathy.com So now let's talk about the H2 blockers. So H2 blockers are a different class, and their primary clinical use is reducing stomach acid production. They're used for heartburn, GERD, and peptic ulcers. But H2 receptors are also present in immune cells and blood vessels. And H2 blockade can modulate immune activity more broadly. In the context of histamine excess, whether from MCAS, histamine intolerance, or hormone-driven mast cell activation, blocking H2 receptors provides a second pathway of histamine suppression that H1 blockers alone don't cover. This dual pathway approach is not new in clinical medicine. Combining H1 and H2 blockade is used in the management of anaphylaxis, chronic urticaria, and mast cell disorders. The application to PMDD is an extension of this logic rather than a novel pharmacological idea. The concern with H2 blockers used long-term is their effect on digestion. Stomach acid is necessary for breaking down food, absorbing key minerals, and producing the acidic environment that protects against certain pathogens. Prolonged H2 blockade can impair absorption of vitamin B12, iron, calcium, and magnesium, and it can reduce gut motility and alter the microbiome. So these are not trivial considerations. If someone is using H2 blockers for a couple of weeks every single month, it can really have a massive knock-on effect. So what's the current evidence and where are the gaps? So it's important to be clear about what we do and don't know here. What we do know, a well-established understanding of the oestrogen and histamine feedback loop from decades of research, evidence from observational studies and clinical case reports that women with PMDD, MCAS, histamine intolerance, or endometriosis can experience relief from antihistamines. Mechanistic plausibility, so the biology makes sense, and a growing body of clinical observation supports the H1 and H2 combined approach, particularly in people who find H1 blockers alone insufficient. What we don't know, a randomized controlled trial testing antihistamines for PMDD. We don't know the long-term safety data for cyclical antihistamine use. So three to six months of the year for potentially many years. Biomarkers that can confirm histamine is a significant driver for any individual patient, so it's still trial and observation. So given the gap, antihistamines for PMDD sits in the category of off-label use grounded in mechanistic reasoning and patient-reported outcomes, which is not unusual in women's health, but it does mean caution is warranted. Now, PMDD in some women is so debilitating. If H1 and H2 blockers are giving you your life back. Honestly, I'm all for it. But often women will do significantly well as in like the PMDD goes from reducing the histamine in the body. And how we do that is we look at all the root causes of histamine. So all the things I could talk about on this show. SIBO, digestive enzyme insufficiency. The Oestrogen detoxification supporting your natural progesterone production. Dealing with oxalates, dealing with mold, dealing with irritable bowel disease, flares, dealing with Helicobacter pylori. So whatever is driving up your histamine in the first place. Perimenopause, it can just sort of happen out of the blue. I have had several patients recently where that's the case, but often there is an underlying driver of histamine that doesn't actually rear its ugly head until sort of late perimenopause. The other thing that we've found clinically is how correcting methylation can be a game changer for women with PMDD. The mechanism is quite different. So women are often overmethylating due to COMT enzyme. And when you're overmethylating, you just build up too many methyl groups. When you have too many methyl groups, it increases dopamine and norepinephrine. Interestingly, methyl groups can break down histamine in the central nervous system, but overmethylating women can have issues regulating their inflammation, and generally inflammation will drive up histamine. And I've seen this often where women are correcting methylation, so taking niacinamide to reduce methyl groups, helping a lot with their general mood and PMDD, and then their skin rash or their sort of acne or sort of more systemic skin-related symptoms significantly improve. So I've definitely seen a link there. I've always considered histamine as part of the picture with PMDD. I've always considered methylation. Without a doubt, there is a connection. We see it clinically all the time. We can often just get the histamine under control by treating the root cause. Supporting methylation, that can really help with PMDD. Now, I have had some women who are extreme. Now we know about these H1 and H2 blockers. You'll need to get it prescribed from a doctor. But If you've tried correcting methylation and working with a practitioner that really understands histamine, and you have gone through a workup of that. If you really want to understand all the causes of high histamine, my second episode talks about all of them. There's often hidden things like mold and oxalate. Sulfur intolerance can drive up histamine. So there's many, many things. Now, H1 and H2 blockers are not without side effects. And, in particular these H2 blockers because H2 blockers, when you reduce your hydrochloric acid, it causes malabsorption. It causes malabsorption of your methylation nutrients. It causes SIBO, which drives up histamine. It does worry me a bit, because it can definitely make a histamine issue way worse in the long run. The bottom line is that histamine is a legitimate part of the biological conversation around PMDD. I mean, we've known this for years. The oestrogen-histamine feedback loop is real. We see it all of the time. It's very, very common. So the mechanistic case for why elevated histamine could amplify PMDD through neuroinflammation, neurotransmit disruption, mast cell activation is very plausible and coherent. We see it clinically all the time. The research just hasn't been done. There's never enough research on what we do, unfortunately. But it makes sense when we think about the mechanisms. The antihistamine approach, particularly combining the second-generation H1 blockers with H2 blockers, it has a logical basis and anecdotal clinical support. So it's important to know that it's not a validated PMDD treatment. This is from allopathy. It doesn't address the underlying drivers. And this is why working with someone like myself that's very versed with histamine and hormones, I really encourage you to do that. You know, if you are really feeling terrible, ladies, I understand. Like, truly, I understand 'cause I've gone through perimenopause into menopause. And I see it in my patients every day. Just if you can take some H1, H2 blockers, if your doctor is willing to prescribe those, just see how you go for a couple of cycles. Three cycles. And if it's significantly helping you, then you have a big histamine issue. And then, you know, if once you're convinced and you- your partner can see it, and your friends can see it, and your doctor can see it, and you can see it, then it will give you clarity that histamine's a big problem, and then we can start addressing all the underlying drivers and hopefully be able to pull you off those meds and treat it naturally. So I'm here to help. I see patients online globally. If you'd like to make an appointment, you can easily do that via my website, joannekennedynaturopathy.com Thank you for joining me. I hope you found this episode beneficial. Be sure to subscribe to The Histamine Well so you don't miss an episode. If this podcast has supported you, one of the most impactful ways to help us reach more people is to leave a review on Apple or Spotify. Take a quick screenshot and email it to us at info@joannekennedy.com.au and as a thank you gift, we will send you a copy of my histamine intolerance e-book. Until next time, take care and be well.