Yes, antihistamines, especially older types like Benadryl and some newer ones like Zyrtec/Allegra, can cause weight gain by increasing appetite, reducing activity through drowsiness, and potentially affecting fat production, as histamine normally helps suppress hunger. While some antihistamines are used specifically to promote weight gain, consistent use of common allergy medications has been linked to higher BMI, although more research is needed to determine which specific drugs are most problematic and why.
H1 receptor antihistamines such as cetirizine, fexofenadine, and desloratadine are among the most commonly prescribed medications for the treatment of allergies and have been shown to stimulate appetite and weight gain as side effects of treatment (6).
Just as taking antihistamines can increase your weight, when you stop taking them, you might notice that you lose some of the added weight.
How to Prevent Weight Gain From Antihistamines
Constipation, blurry vision, and dry mouth are also frequently reported. Rare but serious antihistamine side effects include a higher risk of falls for older adults and trouble urinating. Long-term use of certain antihistamines may also cause severe itching when you stop taking them.
Side effects of antihistamines
Tolerance is not a problem. Rarely, they can cause acute self-limited liver injury. One study has reported a more serious long-term effect, a 3.5-fold increase in the risk of gliomas, a common type of brain tumor in patients with long-term antihistamine use for allergic conditions.
Which Medications Cause the Most Weight Gain?
Stay hydrated: Drinking plenty of water helps your body flush out the medication through your kidneys.
Cyproheptadine (Periactin) is used to relieve allergic symptoms. It is also used to relieve headaches, and motion sickness. It may also be prescribed to your child to increase his or her appetite to help with emptying of the stomach and improve symptoms of nausea and vomiting.
Antihistamine Withdrawal Symptoms Often Include: Anxiety or irritability. Insomnia. Dizziness or lightheadedness.
Classes of medications that are commonly prescribed and are known to cause weight gain include antipsychotics, steroids, diabetes medications, antidepressants, and more.
Weight loss blockers often include calorie creep (underestimating intake), a slowing metabolism as you lose weight, hormonal imbalances (like thyroid or cortisol issues), poor sleep, chronic stress, and not enough protein/too many processed carbs, leading to plateaus; addressing these involves adjusting calorie intake, increasing activity, improving diet quality (more protein/veggies, fewer sugars/refined carbs), managing stress, and ensuring sufficient sleep.
From this survey study, prescription H1 antihistamine users had a significantly higher weight, waist circumference, and insulin concentration than matched controls. The men using antihistamines were around 22 pounds heavier than the nonusers, and the women were nearly nine pounds heavier.
Bloating, or swelling due to a buildup of fluid in the tissues can cause weight gain. This may be due to menstruation, heart or kidney failure, preeclampsia, or medicines you take. A rapid weight gain may be a sign of dangerous fluid retention. If you quit smoking, you might gain weight.
It's thought that beta blockers slow the body's ability to change food into energy, called metabolism. You also might gain a few pounds if you take a water pill called a diuretic but then switch to a beta blocker.
In general, wean gradually by 25-50% of the daily dose every 1-4 weeks. If reason for deprescribing is serious adverse effects, wean faster or cease immediately.
Common symptoms may include:
The quick answer is it takes our body 24 to 48 hours to process the substance. However, it can show up in urine tests up to four days after ingestion. You should understand the timeline of diphenhydramine in your system so you know when to take the next dosage. That's because taking too much causes nasty side effects.
The bottom line
Certain diabetes medications, antidepressants, and antipsychotics are common culprits. Steroids, the birth control shot, and some beta blockers can also cause weight gain. Lifestyle changes, like diet and exercise, may be helpful in managing this side effect.
Vitamin A, B, and D. Protein supplements such as protein shakes or snacks, effectively increase body weight, body circumference, and muscle mass. Creatine for muscle growth and weight gain. Fish oil, including omega-3, to boost appetite.
Medicines that can cause fluid retention
Side effects of first-generation H1 (allergy) antihistamines can include: Drowsiness (sleepiness) and reduced coordination, reaction speed and judgment. Dry mouth and dry eyes. Blurred or double vision.
Fexofenadine (Allegra)
It's one of the least sedating second-generation antihistamines, making it a safe option for long-term use if you take it as your doctor prescribes.
Corticosteroid sprays, also called glucocorticoid sprays, prevent and relieve nasal allergy symptoms. These medicines are very effective on their own for treating ongoing or seasonal hay fever.