Cetirizine for allergies – and why probiotics like LP-33 and GMNL-133 can be a natural alternative

Allergies have long since become one of the most common chronic diseases worldwide. Whether it's hay fever, house dust mite allergy, pet allergy, or allergic asthma – these symptoms can significantly impact everyday life. Symptoms range from sneezing, itchy eyes, and a runny nose to shortness of breath and fatigue. Especially during pollen season, many sufferers turn to antihistamines like cetirizine for relief.

Cetirizine is one of the best-known and most commonly used medications for treating allergies. It works quickly and reliably—but it is often accompanied by unwanted side effects such as fatigue or difficulty concentrating.

However, an interesting field of research has emerged in recent years: certain probiotic strains, particularly Lactobacillus paracasei LP-33 and GMNL-133, have shown comparable effectiveness in allergic symptoms in studies – but without the typical side effects of classic antihistamines.

In this article, we take a closer look at how cetirizine works, its advantages and disadvantages, and why probiotics such as LP-33 and GMNL-133 are considered a promising alternative. We draw on current scientific findings and offer an outlook on new approaches to allergy treatment.

What is cetirizine and how does it work?

Cetirizine belongs to the group of second-generation antihistamines . It specifically blocks the effects of histamine – a chemical messenger released during allergic reactions. Histamine is responsible, among other things, for swelling of the nasal mucous membranes, watery eyes, and itchy skin.

By blocking the histamine H1 receptor, cetirizine prevents the typical allergic symptoms from being triggered. It therefore acts symptomatically , not causally.

The effect usually begins within 30 minutes and lasts for about 24 hours. Therefore, once-daily dosing is sufficient for many patients. Cetirizine is available over-the-counter in pharmacies – in tablet, drop, or syrup form – and is used to treat numerous allergic conditions.

The benefits of cetirizine

There are good reasons why cetirizine is so widely prescribed and recommended. It is well-researched, inexpensive, readily available, and, when used correctly, well-tolerated by most people. Cetirizine provides rapid and noticeable relief , especially for acute hay fever or allergic skin reactions (e.g., hives).

Compared to older antihistamines (e.g. diphenhydramine), cetirizine causes less drowsiness because it only slightly crosses the blood-brain barrier.

But: The dark side – side effects of cetirizine

Despite all its benefits, cetirizine remains a synthetic drug with potential side effects. The most common is fatigue . Depending on the study , up to 20% of users report a certain degree of drowsiness, which can be particularly disruptive in everyday life (e.g., while driving or working). Concentration problems, headaches, and dry mouth are also documented side effects.

Some sufferers also react sensitively to long-term use, for example, in cases of chronic allergies or seasonal hay fever. In such cases, the question often arises: Are there effective alternatives that do not involve chemical exposure – and yet are just as effective?

Probiotics – a new approach in allergy treatment?

The topic of microbiome and allergies has gained enormous importance in medical research in recent years. Our immune system is closely linked to the microorganisms in our gut. A healthy intestinal flora ensures a balanced immune response – whereas a disrupted microbiome is associated with increased susceptibility to inflammation and allergies.

This is where probiotics come in: living microorganisms that, when consumed in sufficient quantities, have a health-promoting effect on the host . Of particular interest to allergy sufferers are the probiotic strains Lactobacillus paracasei LP-33 and GMNL-133 , whose effects have been specifically investigated in several studies.

LP-33 – The pioneer among allergy-relieving probiotics

Lactobacillus paracasei LP-33 is a naturally occurring bacterial strain capable of modulating the immune system . Unlike antihistamines, which directly interfere with histamine activity, LP-33 targets the regulation of the immune response .

Several clinical studies – particularly from Taiwan and Europe – have shown that LP-33:

• can significantly reduce the symptoms of seasonal allergic rhinitis (hay fever)

• improves the quality of life of allergy sufferers

• is well tolerated and does not cause drowsiness

In a placebo-controlled double-blind study, LP-33 users reported significantly less runny nose, sneezing, and itchy eyes – with a comparable effect to cetirizine, but without drug-related side effects.

GMNL-133 – A promising young strain with strong effects

The probiotic strain Lactobacillus paracasei GMNL-133 has also been extensively researched in relation to allergies. GMNL-133 acts via similar mechanisms to LP-33, but in some studies, it has shown even stronger anti-inflammatory effects .

This strain was tested, among other things, in a randomized study with allergic mice, in which the symptoms of allergic rhinitis significantly improved after administration of GMNL-133. The immune system showed improved regulation between TH1 and TH2 cells—a key role in the development of allergies.

Although human research on GMNL-133 is still underway, initial observations indicate that this strain can achieve effects comparable to antihistamines while being well tolerated .

Probiotics vs. Cetirizine – A Scientific Comparison

The following overview shows the key differences and similarities between cetirizine and the probiotic strains LP-33/GMNL-133 in allergy treatment:

Why probiotics not only relieve symptoms but also influence causes

A major advantage of probiotic therapy is that it doesn't just "tinker" with the symptoms, but can also influence the underlying immune dysregulation . Allergies occur when the immune system overreacts—that is, classifies harmless pollen, pet dander, or house dust as dangerous.

Probiotics such as LP-33 and GMNL-133 promote the development of tolerance to allergens by stimulating regulatory T cells and inhibiting pro-inflammatory cytokines. They can therefore also contribute to reducing allergy susceptibility in the long term.

For whom are probiotic alternatives particularly interesting?

• For people who suffer from the side effects of antihistamines

• For children who want to avoid chemical medications as much as possible

• For people with chronic allergies who are looking for a more holistic solution

• For those affected by additional intestinal dysbiosis, irritable bowel syndrome or inflammatory skin diseases

Probiotics can also provide effective protection in preventative measures – for example, before the start of the pollen season.

Conclusion: Cetirizine works – but probiotics can do more

Cetirizine is undoubtedly an effective medication for allergic symptoms. However, its side effects—especially fatigue—often limit its ability to function in everyday life. Studies have shown that Lactobacillus paracasei LP-33 and GMNL-133 have a comparable effect with significantly better tolerability . As natural helpers, they target the immune system and could help better control the cause of allergies in the long term.

The combination of both approaches – short-term relief through cetirizine and long-term stabilization through probiotic therapy – is a sensible approach for many people.

With a healthy microbiome, the body not only becomes more resilient to allergens but also more resistant overall. The gut, as the immune center, is key – not only to digestion but also to allergy-free status.

If you're interested in probiotic allergy therapy, look for scientifically tested strains like LP-33 or GMNL-133 when purchasing and seek advice from a medical professional if necessary. This way, you can not only combat symptoms in the long term, but also strengthen your overall health.