Allergen immunotherapy, commonly known as allergy shots, is a long-term treatment designed to reduce sensitivity to environmental allergens. Since this commitment can span several years, patients often express concerns about potential side effects, including the possibility of weight gain. Understanding the connection between this specific therapy and body weight requires a look at the treatment’s mechanism and how it differs from other medications used for allergy management. This exploration will provide clarity on whether allergy shots themselves contribute to changes in body weight.
How Allergy Shots Work
Allergy shots function similarly to a vaccine, introducing the immune system to small, controlled amounts of the substances that trigger allergic reactions. This process, called subcutaneous immunotherapy (SCIT), aims to build a lasting tolerance to common allergens such as pollen, dust mites, or pet dander. The shots contain purified extracts of these allergens, typically suspended in a saline solution.
Treatment involves two distinct phases: the build-up phase and the maintenance phase. During the build-up phase, injections containing gradually increasing concentrations of the allergen are administered frequently, usually once or twice a week, over a period of three to six months. This slow escalation allows the body to safely adjust to the allergen presence. Once the maximum safe and effective dose (the maintenance dose) is reached, the schedule shifts. Injections are then given much less often, typically every two to four weeks, and this phase continues for three to five years. The ultimate goal is to induce long-term desensitization, altering the immune response to produce “blocking antibodies.”
The Evidence on Weight Gain and Immunotherapy
Current medical and scientific literature does not support a causal link between allergy shots and significant weight gain. The composition of the immunotherapy injections is the primary reason for this lack of association. Allergy shots contain only purified allergen extracts and a saline base, which are biologically inert in terms of metabolic function.
These shots do not contain hormones or compounds known to influence appetite regulation, fat storage, or fluid balance. The mechanism of action is focused on the immune system, specifically on modulating T-cells and decreasing the production of allergy-related antibodies. This immunological shift does not directly interact with the body’s weight control centers.
While any medical intervention carries a risk of side effects, those from allergy shots are overwhelmingly localized reactions, such as redness, swelling, or itching at the injection site. Systemic reactions are rare. There is no clinical evidence to suggest that the treatment alters metabolism or caloric intake in a manner that would lead to weight gain.
Distinguishing Weight Gain from Other Allergy Treatments
The common concern about weight gain and allergy treatment is often valid, but it is frequently misattributed to allergy shots instead of other, more widely used allergy medications. Oral corticosteroids, like prednisone, are a common source of confusion. These powerful anti-inflammatory drugs mimic the stress hormone cortisol, which is known to cause weight gain.
Prednisone can stimulate appetite, leading to increased caloric intake. It also causes the body to retain sodium and water, resulting in fluid retention and swelling. Furthermore, long-term use of these steroids can lead to a redistribution of fat, often resulting in a rounder face and increased abdominal fat deposits. These metabolic effects are a well-documented side effect of systemic steroid use.
Certain antihistamines, particularly some older or specific prescription versions, have also been linked to weight changes. Since histamine is a neurotransmitter that helps regulate appetite in the brain, blocking its receptors can reduce the body’s natural appetite suppression. This effect may lead to increased hunger and caloric consumption over time. Allergy shots, by contrast, do not block histamine receptors; they target the underlying cause of the allergic reaction without these metabolic side effects.