TL; DR: There are a few published case reports and LOTS of stories from long COVID support groups about how antihistamines [(“histamine receptor antagonists” (HRAs)] can decrease long COVID symptoms. While they may help, we need more information to know who they help, when they should be taken, and how they should be taken.
❓What evidence do we have?
In late 2021, an observational study came out that followed 49 people with long COVID to track their symptoms over time, the effect of HRAs on their symptoms, and changes to specific markers in their blood. 26 received HRAs and 23 did not. Among the 26 who did receive HRAs, 19 had improvement in symptoms; of the 23 who did not, only 6 had symptoms improve. Most improved about one month after treatment. In another published article in February 2022, two case reports were published about two women who took HRAs (accidentally) after having recovered from COVID-19. Both women reported improvement in long COVID symptoms and long term use of HRAs. There have also been many discussions and case reports on patient advocacy groups like Survivor Corps.
❓Why would this work and which HRAs did people use?
🦠 Researchers are not completely sure how this works, but there are theories. There are histamine receptors on many cells in the body. A classic way we think about HRAs working is to prevent an anaphylactic type of response (think preventing symptoms of eczema or allergies). But HRAs also work on T cells (white blood cells that help in the immune response) and mast cells (another white blood cell that is found in connective tissues like skin and can help control the body’s response to virus, bacteria, and other threats to the body). Researchers believe that HRAs work in long COVID, not by reducing the anaphylactic type of response, but by helping to keep the immune response down. They hypothesize that this is because of histamine blocking activity on the T cells. Mast cells may also have a role. Symptoms that people reported (and that improved) in the study and case reports mentioned included those like fatigue, rashes, pain, stomach symptoms, and brain fog. It is important to note that one symptom, dysautonomia (poor regulation of autonomic nervous system with symptoms like variable heart rate, blood pressure, sweating), did not get better, suggesting that this is related to a different mechanism.
💊 There are two types of HRAs. H1 receptor antagonists usually help to prevent anaphylaxis and allergic reactions. These are older medications like Benadryl (diphenhydramine) and newer ones like Allegra (Fexofenadine). They decrease the body’s histamine response, which is something that tells your body to rev up the immune response. H2 receptor antagonists work on the digestive system and can decrease the release of stomach acid. These are medications like Famotidine (Pepcid). In the 2021 study, people in the study were given a combination of H1 and H2 receptor antagonists. The two women in the case reports took medications including Benadryl, Allegra, and Hydroxyzine Pamoate (Vistaril).
❓Why is this important?
💰 Antihistamines are widely available and have minimal side effects. They are also low cost. if these prove to be an effective treatment for long COVID symptoms, they could help people recover and be able to live their lives more fully. More importantly, they offer hope for long COVID patients who have limited treatment options available.
⬇️ The bottom line: HRAs MAY help long COVID symptoms. We need more data to better understand which ones work best, for whom, and which symptoms they help with the most. This is still promising because we don’t yet have specific treatments for long COVID. More often than not, long COVID is treated by the symptoms to see what helps. Lifestyle changes are also encouraged. If HRAs are effective, they could be a lower cost and more accessible treatment option for people suffering with long COVID.
🏽 This is hopeful news for people who have suffered with long COVID symptoms and we hope that we will continue to learn more about possible treatments.
Stay safe. Stay well.
Those Nerdy Girls