Pharmacist Reveals 12 Common Drugs that Cause Weight Gain (and Solutions)

Sometimes it’s not all your fault. These commonly used drugs have side effects that may be causing your weight gain or making it difficult for you to lose the weight with diet and exercise.

After more than a decade of working as a Pharmacist I have seen these common drugs sabotage some of the best weight loss efforts out there. 

Today I will show you exactly which of these drugs cause weight gain and prevent weight loss, exactly how much weight you can gain and what you can do to stop this side effect.


The information provided in this article is for informational purposes only and it is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Every individual should always seek the advice of a physician or other qualified health providers with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it based on any information in this article.

1. Weight Gain Side Effects of Corticosteroids: Prednisone(Deltasone,Sterapred), Bethamethasone (Celestone)

Corticosteroids are hormones that are naturally produced by our bodies. Synthetic forms of corticosteroids are used to treat common conditions such as asthma, allergic rhinitis, skin and food allergies. They are also used in many serious autoimmune conditions.

Corticosteroids are well known for causing weight gain. The weight gain is caused by excessive fluid retention (bloating), increased appetite for carbohydrates and sugary meals, and most importantly, corticosteroids play a major role on in slowing down your metabolism.

They cause increased glucose levels and insulin resistance resulting in an increase of fat production and storage of fat especially in the abdominal area. Corticosteroids are also known to redistribute fat from other parts of your body to your mid-section and face.

Almost 70% of patients report weight gain as a side effect with some patients reporting weight gain of up to 8% (15 pounds). The severity of weight gain increases with longer term treatments.

The weight gain caused by corticosteroids can be controlled by changing to newer therapies, using the lowest doses possible or changing to topical and local treatments were possible.

For those with serious conditions that are unable to change their medication it is advised to start a low carbohydrate high protein diet, resistance training and decrease salt intake to best prevent the weight gain.

2. Weight Gain Side Effects of Anti-Depressants (Zoloft, Abilify, Prozac, Paxil)

    Anti-Depressants are mostly used for depression however they are now commonly used for other conditions that include OCD, anxiety, and PTSD.

    Anti-Depressants cause weight gain by increasing appetite and preventing the feeling of fullness. This causes us to eat more and not know when to stop eating resulting in a significantly greater amount of food required at each meal. They also trigger cravings for carbohydrates and sugary junk food.

    About 25% of patients experience excessive weight gain with many patients reporting weight gain of up to 20 pounds.

    The weight gain experienced from the different types of anti-depressants differ widely with the SSRI’s causing the greatest weight gain. Efexor, Serzone and Welbutrin have no weight gain side effects while the SSRI’s such as Paxil, Prozac, Zoloft and Abilify have been proven to cause the most weight gain.

    Resistance training and High Intensity Interval training have both shown improved outcomes for weight gain and depression. High fat and protein diets are also beneficial for depression and weight loss.

    You can also consult your physician to discuss changing your medication to one of the drugs that cause less weight gain. Some physicians add in low doses of Welbutrin and Naltrexone which seems to stop the appetite inducing effects of the anti-depressants.

    3. Weight Gain Side Effects of Anti-Histamines: Diphenhydramine(Benadryl), Carbinoxamine (Clistin), Clemastine (Tavist), Chlorpheniramine (Chlor-Trimeton), and Brompheniramine (Dimetane)

    Anti-histamines are used for colds, flus, and allergies. They are the most commonly used of all the drugs on this list.

    Histamine is an important chemical that acts on our brain to suppress appetite and regulate food intake. When we use an anti-histamine drug we essentially block histamine from suppressing our appetite. This results in a massive increase in hunger and cravings resulting in uncontrollable food intake.

    This effect of anti-histamine is so strong that the anti-histamine Cyproheptadine (Periactin) is commonly used to increase appetite in cancer patients.

    Secondly, histamine plays a role in fat breakdown and anti-histamines block that effect causing the accumulation of fat and weight gain.

    Anti-histamines also cause sedation which slows you down and keeps you inactive causing even further weight gain.

    One study showed that males using antihistamines were on average almost 22 pounds heavier than those that did not use anti-histamines and their female counterparts were almost 11 pounds heavier.

    Fortunately, most anti-histamines are used to treat mild conditions and changing them or omitting their use will not have a significant impact on your health.

    You also have the option of changing to the newer second and third generation anti- histamines that don’t cause weight gain.

    4. Weight Gain Side Effects of Risperidone (Risperdal)

    Risperdal is an antipsychotic drug that is now commonly used for bipolar disorder, obsessive compulsive disorder and to treat irritability in social disorders.

    It causes weight gain by increasing appetite in a similar manner to anti-histamines leaving you with a permanent feeling of hunger. It also causes fatigue and sleepiness making you constantly tired and prone to inactivity. It also increases the frequency and intensity of cravings for junk food. Most significantly, it affects leptin and glucose levels resulting in greater fat storage.

    One study showed an increase in weight by an average of 15% (11.9 pounds) This increases as the duration of the treatment continues.

    Talk to your physician about any newer drugs available to treat your condition. The biggest problem with Risperdal is not being able to control your portions or not knowing when to stop eating. Plan your meals in advance and aim to stick to your limited portions. Start a resistance training program which has been proven to have marked effects on improving mental health.

    5. Weight Gain Side Effects of Beta blockers: Propranolol (Inderal LA, InnoPran XL), Atenolol (Tenormin)

    Beta Blockers are used for hypertension, anxiety, glaucoma and in some migraine prevention products.  

    These drugs cause weight gain by reducing your metabolism. Beta Blockers can decrease energy expenditure by up to 9% and reduce your basal metabolic rate by up to 12%. Beta Blockers also reduce fat breakdown and promote insulin insensitivity all leading to increased weight gain.

    Patients have reported weight gain of up to 7.7 pounds.

    B-blockers are really old drugs and there are so many newer treatments that don’t cause weight gain. Speak to your doctor about changing your treatment.

    6. Weight Gain Side Effects of Vitamin B12

    The main symptom of a Vitamin B12 deficiency is the loss of appetite and a decrease in the taste sensation of food leading to weight loss from decreased caloric intake.

    Vitamin B12 is involved in a chemical process in the brain that decreases the levels of histamine. This decrease in histamine has an appetite stimulant effect on our brains and we experience increased sensations of hunger.

    A 50% increase in Vitamin B12 levels can cause up to a 25% increase in calorie intake.

    Vitamin B is found in most vitamin supplements and even fortified in many foods, so be vigilant about taking too much of Vitamin B.

    7. Weight Gain Side Effects of Birth Control: Progesterone (Provera)

    Progesterone only birth control pills are commonly used by women that are unable to tolerate estrogen and also in women that have a high risk of breast cancer.

    Progesterone is known to increase appetite, and many women will testify to this effect during the last week of their menstrual cycles when progesterone levels are at their highest.

    Progesterone also promotes the retention of sodium which causes bloating and further weight gain.

    The effects of progesterone on weight gain is more prominent with injectable progesterone contraceptives compared to oral contraceptives.

    The weight gain from progesterone only contraceptives are experienced by 25% of users with an average weight gain of around 17.6 pounds after 12 months.

    There are many other options available for contraception which are best discussed with your doctor.

    Try staying on a low sodium low carbohydrate diet to fight the bloated weight gain caused by progesterone.

    8. Weight Gain Side Effects of Cannabis: Nabilone(Cesamet), Dronabinol(Marinol)

    Medicinal Cannabis has become an effective treatment option for many conditions including neuropathic pain, muscle spasms, nausea, epilepsy and as a powerful appetite stimulant.

    Cannabis has been shown to increase levels of the hunger hormone ghrelin. This results in an intensely increased appetite, especially cravings for high carbohydrate meals.

    Participants in one study gained an average of 7.7 pounds when cannabis treatment was initiated.

    Take your cannabis medication after you eat to decrease the appetite stimulant effects of cannabis.

    9. Weight Gain Side Effects of Valproic acid (Depakene, Stavzor, Depakote)

    Valproic acid is used to treat epilepsy and migraines. Valproic acid increases insulin secretion promoting energy storage as fat which results in weight gain.

    It also affects ghrelin which increases hunger, cravings and binge eating. Valproic acid also causes both insulin and leptin resistance, two factors that are directly associated with obesity.

    A study reported that 57% of people taking valproic acid gained an average weight of 19.4 pounds for women and 17.4 pounds for men.

    Patients on valproic acid must engage in more activity and start an eating plan that will help them overcome the powerful cravings and hunger caused by this drug.

    10. Weight Gain Side Effects of Chlorpromazine (Thorazine, Omarzine)

    Chlorpromazine is a psychological drug that is commonly used to treat bed wetting, nausea, hiccups, vomiting, and anxiety.  Like other psychological drugs it plays a role on histamine levels in the brain causing massive increases in hunger and cravings.

    Patients on these drugs for longer term use have experienced an average increase in weight of about 11 pounds with some patients gaining up to 16.5 pounds.

    There are many newer alternatives to chlorpromazine, speak to your Physician about changing your treatment.

    11. Weight Gain Side Effects of Amitriptyline (Elavil, Endep,Vanatrip)

    Amitriptyline is an old anti-depressant that is now commonly used for pain management, anxiety, and other nerve related problems.

    Like the other anti-depressants mentioned earlier it increases hunger and slows down your metabolism.

    It was reported that 30% of people taking amitriptyline for migraines gained more than 5% of their body weight in 26 weeks.

    Amitriptyline is an old drug and there are many newer drugs that can replace it with less side effects.

    12. Weigh Gain Side Effects of Pregabalin (Lyrica)

    Pregabalin is used in pain management associated with damaged nerves. It usually forms part of long a long-term treatment plan and it is also used post-operatively for certain procedures.

    Pregabalin causes weight gain by increasing appetite, slowing down metabolism and water retention.

    41% of patients on Pregabalin gained more than 11 pounds after 6 months of use.

    It must also be noted that patients on Pregabalin are usually in a lot of pain and activity levels are severely diminished.

    In this situation, it is best to concentrate on strict dietary measures to help prevent weight gain. Patients should decrease their total food intake to adjust for the decreased activity levels and salt intake should be limited to offset the water retention caused by Pregabalin.


    As always, consult your physician before making any changes to your drug treatment protocols.

    If you are not losing weight with diet and exercise and you are thinking about adding in a vitamin, supplement or pharmaceutical to help you reach your weight loss goals, please check out my Personalised Weight Loss Consult and Report.


    Older Post Newer Post

    Leave a comment