There are several factors that contribute to weight gain (or carrying excess weight), including inherited genetics, sleep disorders and/or chronic sleep deficiency, chronic lack of exercise and physical activity, nutritional imbalances (including excesses and deficiencies) and chronic high stress, to name a few. One often overlooked factor is medication, or the side effects of taking certain medications (both prescription and over-the-counter).

Below is a list of medications that are commonly correlated with an increase in bodyweight. Note that correlation doesn’t always equal causation. For example, people who take allergy medication may be predisposed to gaining weight not as a side effect of the medication, but because their allergies make exercise more difficult, leading them to exercise less than those without allergies.

That said, many of the medications below do influence a person’s physiology in such a way as to lead to weight gain. Some of these physiological effects include increasing appetite (often by changing hormone levels), fluid retention (sometimes because of medication-induced damage to the kidneys, which regulate body fluid levels), and lower metabolism or less energy (which often leads to less physical activity, which contributes to weight gain).

The drug classes/types below are listed in alphabetical order (ex. allergy then birth control then blood pressure, etc.).


Drugs of interest here include diphenhydramine (an active ingredient in Benadryl, PediaCare Children’s Allergy, Sominex, Unisom, and Tylenol PM), fexofenadine (active ingredient in Allegra), cetirizine (active ingredient in Zyrtec) and other antihistamines (including meclizine, loratadine and cyproheptadine).

Blocking histamine can disrupt an enzyme in the brain that helps regulate appetite, potentially leading to increased food consumption (leading to increased weight gain). Indeed, some older antihistamines (such as cyproheptadine/Periactin), have been used for the expressed purpose of increasing appetite (and therefore, weight gain) in underweight children and cancer patients undergoing chemotherapy.

In addition to their effects on hormones and appetite-regulating brain chemicals, antihistamines like Benadryl have side effects like drowsiness (which may lead to a lack of physical activity) and water retention (leading to water weight gain). A 2010 study found that people taking antihistamines like Allegra and Zyrtec were 55% more likely to be overweight than those not taking the drug. And as you might guess, chronic use of antihistamines is known to exacerbate medication-induced weight gain. [1-8]



Functionally-speaking there are 6 ways of delivering hormonal birth control to women: the pill, the patch, the implant (ex. Nexplanon/etonogestrel), the shot (ex. Depo-Provera/medroxyprogesterone acetate), the ring and the IUD. All 6 of these methods use either progestin (a synthetic analog that resembles the structure of the natural hormone progesterone) or a combination of progestin and estrogen (ex. Ortho Tri-Cyclen) as a means of preventing pregnancy (one non-hormonal IUD, ParaGard, uses copper as a spermicidal agent).

How does hormonal birth control work? Its starts with gaining a general understanding of what’s happening physiologically and hormonally during a woman’s cycle (I’m using approximations for the days during a typical 28 day cycle). The first part of the cycle is generally referred to as the Menstrual Phase (or bleeding phase or period). This phase typically lasts 3-7 days. It’s during this time that the body is shedding the uterine lining that was being built up during days 7-28. During a woman’s period (days 1-7) the sex hormones estrogen and progesterone are generally low, as are the gonadotropic hormones FSH (follicle stimulating hormone) and LH (luteinizing hormone). It is during this time that the ovaries are working to develop and select a dominant egg. After the bleeding phase (around day 8) estrogen levels begin to rise, and the uterine lining begins to build and thicken, with estrogen levels peaking around day 13. From day 13-15 (the Ovulation Phase) the ovaries are releasing the dominant egg, and FSH and LH levels temporarily spike, while progesterone levels begin to rise dramatically (estrogen levels generally plummet during this phase). For about a week (days 15-23) the uterine lining continues to build, and progesterone levels continue to rise, as do estrogen levels. If no fertilization occurs, the uterine lining starts to break up, and estrogen and progesterone levels drop significantly from day 23-28. See the visualization below…

When a woman is pregnant, the sex hormones progesterone and estrogen are elevated well above even the highest levels achieved by the body during a normal/non-pregnant menstrual cycle. The elevated estrogen and progesterone work to suppress the ovaries from producing and releasing more eggs, and keep the uterine lining thick, both of which safeguard against the possibility of sperm fertilizing another egg (if the woman is sexually active during pregnancy that is). With hormonal birth control, by continually taking progestin (synthetic progesterone) or a combination of estrogen and progestin, the body is, in a sense, “tricked” into thinking it is pregnant, which shuts down ovulation and thickens the uterine lining (thus generally preventing the possibility of getting pregnant).

Some controversy exists over whether hormonal birth control contributes to weight gain. Most researchers agree that Depo-Provera (e.g. The Shot) and Nexplanon directly contribute to weight gain. After that there is considerable disagreement over whether other hormone-based birth control medications commonly contribute to weight gain. To get some clarity on the matter, let’s examine the two hormones we’re talking about individually…


While some research has linked estrogen as having some cardio-protective qualities, some of the side effects of excess estrogen (and sex hormone imbalance) are increases in body fat, water retention and bloating. Taking an estrogen-and-progestin-based birth control medication could contribute to excess estrogen (and weight gain, water retention and/or bloating) IF the amount of estrogen is high enough, and the body’s estrogen-to-progesterone balance is off (i.e. estrogen dominance).


One of the problems here is that progestin (synthetic) is not the same as progesterone (natural), and outside the uterus its effects in the body can be quite different. While progesterone generally opposes estrogen outside the uterus, progestin can sometimes mimic estrogen, leading to water retention, bloating and weight gain. Additionally, the most frequently prescribed synthetic progestin in the U.S. (medroxyprogesterone acetate or MPA) has been tied to an increased risk of cardiovascular disease.

My conclusion- the likelihood of weight gain, bloating and/or water retention is greater when taking any of the commonly available forms of hormonal birth control. For those desiring birth control, I would encourage the consideration of non-hormonal IUDs (ex. ParaGuard) and/or natural family planning (NFP). For those not married I would encourage (big gasp!) abstinence. [2-6, 9-12]

“And God blessed them (Adam & Eve) & said to them, ‘Be fruitful & multiply & fill the earth & subdue it.’” ~Genesis 1:28 ESV

“Behold, children are a heritage from the Lord, the fruit of the womb a reward. Like arrows in the hand of a warrior are the children of one’s youth. Blessed is the main who fills his quiver with them!” ~Psalm 127:3-5 ESV


Conventional medicine’s first-line treatment option for most patients with high blood pressure (hypertension) is diuretic medication, specifically thiazide diuretics. If diuretic medication is not well tolerated, beta blockers, calcium channel blockers and ACE inhibitors are generally next up.

As far as medication-induced weight gain goes, the primary culprits here are generally beta blockers like propranolol (active ingredient in Inderal, InnoPran, Pronol), metoprolol (active ingredient in Lopressor, Toprol) and atenolol (active ingredient in Tenormin). More rarely the beta blocker amlodipine (active ingredient in Norvasc), the calcium channel blocker verapamil (active ingredient in Verelan, Calan) and the alpha-adrenergic agonist clonidine (active ingredient in Catapres) may cause weight gain.

These medications are known to cause a 5-7lbs weight gain during the first few months of being used. The weight gain is suspected to be at least partially related to the drug’s effect on heart rate (slows it down), leading to decreased metabolic rate and increased likelihood of fatigue, which can lead to decreased exercise capacity and exercise frequency. Some research suggests that hypertensive drug-related weight gain may be related to fluid retention resulting from possible drug-induced damage to the kidneys. [1-7]


The first-line medication for most patients with type 2 diabetes is metformin (often marketed under the brand name Glucophage). Metformin, the most frequently prescribed diabetes medication, generally does not promote weight gain, and some even report weight loss while taking metformin. However, there are some potentially serious side effects that can result from taking metformin, including lactic acidosis (where lactic acid builds up in the body and the renal system isn’t able to process and remove it). Individuals with pre-existing liver and/or kidney conditions are more at risk of developing lactic acidosis while taking metformin. Another more common but less serious side effect is gastric upset (heartburn, gas, nausea, stomach pain, etc.). Additionally, metformin doesn’t work in about 25% of cases and loses its effectiveness over time.

After metformin, the second-line medications for diabetes include insulin, thiazolidinediones, sulfonylureas and meglitinides. The problem with many of the drugs in these classes are that they promote weight gain in those who take them. Some of the most common culprits include insulin (active ingredient in Humalog, Novolog, Apidra, Lantus), thiazolidinediones (TZDs) like pioglitazone (active ingredient in Actos), rosiglitazone (active ingredient in Avandia), most of the sulfonylureas including glipizide (Glucotrol), glyburide (Diabeta), tolbutamide (Diabinese) and some of the meglitinide drugs.

Besides contributing to unhealthy weight gain, some of these drugs also carry other potentially deadly side effects. Take rosiglitazone (Avandia) for instance. One study found that people who took rosiglitazone for at least 12 months increased their risk of heart failure and heart attack by 109% and 42%, respectively. As far as diabetes drug-induced weight gain is concerned, the amount of weight gained because of the drug varies considerably, depending on the person, the drug involved and the dose. A 5lb weight gain over the course of 3 months is common for the medications mentioned above, but some patients can gain as much as 20lbs over the first 3-6 months of “treatment.”

Many of these drugs work by stimulating insulin production in the body (or in the case of insulin medication, simply taking insulin itself). One of insulin’s effects is lowering blood sugar by moving blood glucose into glycogen stores or adipose tissue (body fat). It’s clear that “pushing” excess glucose into adipose tissue with insulin can and often does lead to increases in weight and body fat. Additionally, this action can cause blood sugar levels to drop to very low levels (hypo-glycemia), to which it’s often recommended that the patient then consume a HIGH CARBOHYDRATE item (candy, fruit juice, etc.), which itself is one of the main reasons type 2 diabetes develops in the first place (excessive and unbalancing carbohydrate consumption). [1-7, 13-15]