Bariatric Surgery and Medication Use

Full update March 2018

Obesity, defined as a body mass index (BMI) of 30 kg/m2 or more, is rampant in North America. It is estimated that more than one-third of all adults in the United States and more than one-quarter of adults in Canada are obese.1,2 Obesity is associated with many diseases including cardiovascular disease, stroke, type 2 diabetes, and hypertension. In addition, it has been associated with dyslipidemia, some types of cancer, obstructive sleep apnea, osteoarthritis, and some gastrointestinal diseases.1 Helicobacter pylori commonly occurs in this patient population, especially in high-prevalence areas. Patients who test positive will likely be discharged on an eradication regimen.15 Weight loss via bariatric surgery is becoming more common. Bariatric surgery is an option for patients with a BMI of 30 to 35 kg/m2 who do not achieve sustained weight loss and improvements in co-morbidities due to obesity with nonsurgical methods (≥40 kg/m2 or ≥35 kg/m2 with severe comorbid disease [Canada]).2,3 Bariatric surgery leads to weight loss by either decreasing the absorptive capacity of the gastrointestinal tract (malabsorptive surgery) or by limiting food intake (restrictive surgery), or a combination of both. The charts below discuss medication considerations and therapeutic monitoring in patients who have bariatric surgery.

Table 1: Types of Bariatric Surgery

Type of Surgery


Biliopancreatic diversion with or without duodenal switcha

Malabsorptive and restrictive surgery.1,4,5

In the duodenal switch, the small intestine is rearranged to separate the flow of food from the flow of bile and pancreatic juices.1,4,5

Food, bile, and pancreatic juices interact only in the last 18 to 24 inches of the intestine, allowing for malabsorption.1,4,5

Often performed in conjunction with gastric stapling or gastric bypass.1,4,5

Gastric bandinga
(e.g., Lap-Band, others)

Restrictive surgery.4,5

Prosthetic band, placed at the stomach entrance, compartmentalizes the proximal stomach, creating gastric restriction.4,5

Band is typically placed laparoscopically.4,5

Sleeve gastrectomya

Restrictive surgery.1,4,5

Becoming the most commonly performed surgery.36

Stomach is surgically reduced to 25% to 40% of original size.1,4,5

Remaining small part of the stomach looks like a tube or sleeve and leads to the intestine.1,4,5

Sometime performed in people who are too obese or sick to have more invasive weight loss surgeries and are not candidates for gastric banding.1,4,5

Once patients reach a weight to safely undergo surgery, gastric bypass can be performed.1,4,5

Roux-en-Y gastric bypassa

Restrictive (majority) and malabsorptive surgery.1,4,5

Malabsorptive component varies based on length of Roux-limb.1,4,5

Jejunum is connected to the proximal part of the stomach, bypassing most of the distal stomach and proximal small intestine.1,4,5

Proximal Roux-en-Y allows more than two-thirds of functional small intestine to be in contact with food, thereby reducing nutrient deficiencies.1,4,5

Distal Roux-en-Y gastric bypass usually reserved for extremely obese.1,4,5

Performed laparoscopically or through traditional open surgery.1,4,5

Vertical banded gastroplastyb

Restrictive surgery.30

Upper stomach, near the esophagus, is stapled vertically creating a small pouch along the inner curve of the stomach.30

Pouch outlet to the rest of the stomach is restricted with a band, delaying food from emptying out of the pouch.30

Jejunoileal bypass

(no longer performed)4

Prototype of malabsorptive surgery, but no longer performed.4

Connected intact stomach to terminal ileum bypassing most of small intestine, causing profound malabsorption.4

  1. One of the most common surgeries according to the American Society for Metabolic and Bariatric Surgery.
  2. Rarely performed, under review by the Pathway for Approval of New Devices and Procedures Committee within the American Society for Metabolic and Bariatric Surgery.

Table 2: Medication Issues in the Acute Post-Operative Period

(applies to all bariatric procedures)

Medication Issue


Dosage form

For up to two months postoperatively, all medications should be given in a liquid dosage form, a crushed tablet, or an opened capsule:4,6,7

  • Use caution with liquid dosage forms that contain sucrose, corn syrup, maltose, fructose, lactose, honey, mannitol, or sorbitol to avoid issues of dumping syndrome.
  • If a tablet must be used, start with the smallest tablet available.
  • Keep solid dosage forms smaller than an M&M’s candy.

Consider use of non-oral dosage forms (e.g., sublingual, intranasal, rectal, subcutaneous, transdermal).4,6,7

Drugs with narrow therapeutic index

(e.g., tacrolimus, sirolimus, mycophenolic acid, warfarin, etc)

Increase monitoring of serum concentrations or other indicators of efficacy or toxicity.8

A small study (n=27; 22 with Roux-en-Y and 5 with gastric banding) found that warfarin requirements declined in the immediate post-operative period, but returned to pre-operative doses within three to six months.27


Monitor blood pressure closely.

Blood pressure reductions may be seen before weight loss occurs, as early as one week post-op.31

Immediately post-op, consider holding one or more blood pressure meds to avoid low blood pressure.31

Long-term, patients need dosage reduction or can discontinue antihypertensive meds.9-11,31

Diabetes medications

Monitor blood glucoses closely and adjust medications appropriately.4,9-12,31

Blood glucose reductions are usually seen before weight loss occurs.4,9-12

Proactively adjust doses immediately post-op to reduce the risk for hypoglycemia.31

Prior to surgery or immediately post-op:32

  • Discontinue sulfonylureas, meglitinides, or mealtime insulin.
  • Decrease basal insulin doses by about 50% to 75%.

Long-term, many patients need dosage reduction or can discontinue diabetes meds.4,9-12,31

Pain control

Opioids are commonly used to manage post-op pain.32

Recommend adding scheduled oral or rectal acetaminophen as part of the multimodal pain approach to limit the amount of opioids needed.32

Recommend avoiding use of all NSAIDs due to risk of ulceration and perforation.32

Venous thromboembolism prevention

Patients undergoing bariatric surgery are at high-risk for venous thromboembolism.4,13,31

Recommend mechanical prophylaxis along with low molecular weight (LMWH) or unfractionated heparin.15

  • LMWH is preferred. For specific dosing of low molecular weight heparin, see our chart, LMWH Dosing in Special Populations.32
  • If unfractionated heparin is used, recommend a dose of 5,000 units every eight hours.32
  • Consider continuing therapy for up to four weeks in patients after a Roux-en-Y gastric bypass, or in high-risk patients (e.g. previous thromboembolism).32

Table 3: Medications That Should be Avoided or Used with Caution in Patients After Bariatric Surgery

(applies to all bariatric procedures unless otherwise noted)

Medication Class

Reason to Avoid/
Use Cautiously


Bisphosphonates, oral (e.g., alendronate [Fosamax], risedronate [Actonel], others)

Increased risk of upper gastrointestinal irritation.14

Due to the potential for reduced calcium/vitamin D (especially with malabsorptive surgeries) osteoporosis may be a concern.14

Avoid oral bisphosphonates, if possible, in all types of bariatric surgery, especially when patients have a history of GI complications after surgery.14

Recommend alternative parenteral osteoporosis treatment options (e.g., Reclast, Boniva [both U.S.], Aclasta [Canada]), teriparatide [Forteo], raloxifene [Evista] for women.14

If bisphosphonates are necessary, ensure that calcium and 25-hydroxyvitamin D (25-OH) levels are corrected before therapy begins.6,14,15

Ethanol (Alcohol)

In one study, increased rate and extent of absorption following Roux-en-Y gastric bypass.16

Effects of other surgeries not known.16

Counsel patients regarding potential effects of alcohol ingestion.16

Alcohol abuse sometimes develops after any of the surgery types, but especially after Roux-en-Y gastric bypass, possibly due to quicker absorption.31

Enteric-coated and extended-release medications

May have altered release characteristics.4,6,14

Use immediate-release, plain (not enteric-coated) medications or alternate route of administration (e.g., sublingual, transdermal, etc) in all surgery types immediately after procedure.14

Monitor effect of medication if use of extended-release or enteric-coated formulation is unavoidable.14

Avoid long-term in Roux-en-Y gastric bypass and biliopancreatic diversion with or without duodenal switch due to potential for erratic absorption.4,6,14

Medications for Diabetes

With weight loss, insulin resistance declines and the need for diabetes therapies may decline.

Monitor blood glucose closely and adjust medications, especially early after surgery when oral intake is limited.4,9-12,31

Avoid meds that cause hypoglycemia (e.g., sulfonylureas, meglitinides).31

Consider use of metformin after surgery (but avoid in dehydration) and watch for gastrointestinal side effects (e.g., diarrhea).31

Decreased need for diabetes medications seen before weight loss occurs.4,9-12,

Many patients need dosage reductions or discontinue meds over time, as weight loss occurs.4,9-12,31

Avoid thiazolidinediones, due to potential for weight gain.31

There are no data available about safety and efficacy of glucagon-like peptide-1 (GLP-1) agonists or dipeptidyl peptidase-4 (DPP-4) inhibitors after bariatric surgery.31

Medications for Hypertension

With weight loss, blood pressure may go down and unless antihypertensives are reduced, hypotension may occur.31

Monitor blood pressure and titrate or discontinue medications, as weight loss occurs.15,31

Medications for Hyperlipidemia

There are little data available on the effects on lipids.31

Monitor serum lipid profile and titrate or discontinue medications, as necessary.15,31

Nonsteroidal anti-inflammatory drugs (NSAIDs) and Corticosteroids

Increased risk of injury to pouch by either direct effect of medication (NSAIDs) or by systemic effect (prostaglandin inhibition [NSAIDs and steroids]).

Avoid NSAIDs with all surgery types.32

  • Consider use of proton pump inhibitor if an NSAID must be used.4,6,11,14,15,32
  • Alternatives include acetaminophen, opioids, tramadol, or topical NSAIDs (local relief).14,32
  • Celecoxib (Celebrex) may be less toxic and is used by some experts.32

Consider limiting use of corticosteroids if possible, as they may impair healing and can cause ulcers.34

See chart, Safety Comparison of NSAIDs, for GI risk potential.

Oral Anticoagulants

There is an increased risk of venous thromboembolism due to obesity, surgery, and immobility. Changes in dietary intake pre- and post-surgery may change oral anticoagulant medication requirements.


  • Requirements may be reduced for about six months due to reduced intake of vitamin K with liquid diets.31
  • Consider empirically reducing the dose, monitoring, and adjusting as needed.31
  • Most patients return to pre-surgery doses within three to six months post-surgery.27,31

Direct Acting Oral Anticoagulants (DOACs)

  • Data are not available to support use of the DOACs in this patient population.31,35
  • Edoxaban and rivaroxaban are primarily absorbed in the proximal small intestine, and absorption could be reduced with the Roux-en-Y gastric bypass.31
  • Apixaban absorption is likely unaffected by bariatric surgeries, as absorption primarily occurs in the colon.31,35
  • Consider avoiding dabigatran, due to its higher rate of GI-related adverse effects (e.g., dyspepsia, esophagitis) and isolated reports of failure in patients undergoing Roux-en-Y gastric bypass or with short-bowel syndrome.31,35

Medications that cause weight gain

Medications can cause weight gain by a variety of mechanisms including increased appetite and fat tissue.

Avoid, if possible.7,15,19

Medications that cause gastroesophageal reflux
(e.g., calcium channel blockers, beta-blockers, nitrates, tricyclic antidepressants, some antihistamines, etc)

Increased risk of gastroesophageal reflux, especially following “restrictive” surgeries such as gastric banding and Roux-en-Y gastric bypass.6

Avoid, if possible.6

If unable to avoid, use the lowest effective dose.6

Oral Contraceptives

Obesity-related infertility may improve over time, and women are more likely to conceive. Oral contraceptives may be less effective in women after malabsorptive surgery because they undergo enterohepatic recirculation, which may be altered after surgery.31

Women should not get pregnant for at least 12 to 18 months after surgery.31

After restrictive procedures, any of the hormonal contraceptives can be used, as long as there are no reasons to avoid use (e.g., smoking, breastfeeding, thromboembolic risks).28,29

After malabsorptive procedures (e.g., Roux-en-Y gastric bypass or biliopancreatic diversion), recommend avoiding progesterone-only pills and combined oral contraceptive, due to reduced efficacy associated with decreased absorption.28,29,31

  • Some recommend intrauterine devices first-line.31
  • Injectable/implanted progestin can also be considered.31
  • Patches may have reduced adherence due to flaccid skin after rapid weight loss.31

Women using a diaphragm prior to surgery, may need refitting as weight loss occurs.17,31

See our chart, Contraception for Women With Chronic Medical Conditions, for more on options in obese patients and patients with other risk factors (e.g., age, smoking).

Medications associated with gallstones
(e.g., gemfibrozil)

Rapid weight loss and certain meds can be associated with development of gallstones.6

Avoid, if possible.6

Some recommend ursodiol (Actigall [U.S. only], Urso) 300 mg to 500 mg daily for six months after surgery as prophylaxis, even in patients not taking meds that increase the risk for gallstones.6,33

Products containing sorbitol and other nonabsorbable sugars.

Increased risk of dumping syndrome (symptoms of nausea, pain, diarrhea, sweating, tachycardia, fainting usually 30 minutes to three hours after ingestion).

More common following Roux-en-Y gastric bypass.18,31

Recommend limiting high-sugar foods and medications, including lactose or other nonabsorbable sugars, as these may worsen symptoms.6,18

Use caution with liquid dosage forms that contain sucrose, corn syrup, maltose, fructose, lactose, honey, mannitol, or sorbitol to avoid issues of dumping syndrome.4,6,7

Medications that require food and/or gastric acid for optimal bioavailability.

Examples may include:20,21

  • carbamazepine
  • cefpodoxime tablets
  • cefuroxime
  • cinacalcet
  • duloxetine
  • griseofulvin
  • isotretinoin
  • ketoconazole
  • mefloquine
  • nitazoxanide
  • phenytoin
  • posaconazole
  • selegiline
  • valganciclovir
  • vilazodone
  • telaprevir
  • ziprasidone

Bariatric surgery may decrease bioavailability because of lack of food/acid in the stomach.14

  • Roux-en-Y gastric bypass may produce relative achlorhydria.14

Use caution when using these meds.20,21

Monitor treatment response.20,21

Consider alternatives, if adequate response not achieved.20,21

Table 4: Medications That Should be Recommended in Patients After Bariatric Surgery

(deficiencies may be more common in malabsorptive surgeries vs purely restrictive surgeries)24

Medication Class

Reason to Recommend


Multivitamin supplements

After some bariatric procedures, especially malabsorptive surgeries, there may be reduced absorption of some vitamins/minerals.

Patients who undergo gastric banding should take a multivitamin supplement that supplies 100% of the daily value for at least two-thirds of the nutrients.22

Patients may need up to 200% of the daily value of some components sometimes based on the surgical procedures.34

  • Specific recommendations for individual components are outlined below.

In the immediate post-operative period, a liquid preparation or chewable tablet should be used.22

Calcium and vitamin D supplements

Calcium requires acid environment for dissolution and subsequent absorption in duodenum and proximal jejunum.14

Roux-en-Y gastric bypass may produce relative achlorhydria.14

  • All patients should be screened for calcium and vitamin D deficiency before surgery.34
    • A combination of tests may be necessary and can include vitamin D, 25-hydroxyvitamin D (25-OH), serum alkaline phosphatase, parathyroid hormone (PTH), or a 24-hour urine calcium.34
  • Monitor all patients after surgery, with 25-OH (preferred) and PTH.
  • Calcium citrate (with or without meals) may be the preferred salt, especially in patients who have undergone Roux-en-Y gastric bypass.31
    • However, if cost is an issue, consider calcium carbonate (with meals).

Calcium supplementation

  • Recommend calcium doses based on specific surgery:34
    • 1,200 mg to 1,500 mg daily (divided doses) following Roux-en-Y gastric bypass and gastric banding
    • 1,800 mg to 2,400 mg daily (divided doses) following biliopancreatic diversion in combination with a vitamin D supplement.
  • In the early post-operative period, a chewable tablet or liquid preparation should be used. 6,11,14,15,22
  • Divide doses (e.g., 500 mg/dose) and spread out throughout the day for best absorption.34
  • Separate doses from iron or multivitamin supplements by at least two hours.37

Vitamin D supplementation

  • Recommend vitamin D 3,000 IU/day for most patients, though doses may vary based on serum levels.34
    • Higher doses may be needed with significant deficiencies (e.g., 50,000 IU one to three times weekly).31

Fat-soluble vitamins (A, E, and K)*

*Vitamin D is discussed with calcium supplements above.

Decrease in fat absorption can lead to deficiency in fat-soluble vitamins.14

Vitamin deficiencies are more common with malabsorptive than restrictive procedures (e.g., Roux-en-Y gastric bypass and biliopancreatic diversion).14

  • Recommend screening (signs, symptoms, and labs) all patients for deficiencies prior to surgery.34
    • Vitamin A: retinol binding protein, plasma retinol
    • Vitamin E: alpha-tocopherol
    • Vitamin K: des-gamma-carboxy prothrombin
  • Monitor for vitamin A deficiency within one year after surgery, especially after Roux-en-Y gastric bypass and biliopancreatic diversion.
  • Monitor symptomatic patients for possible vitamin E or K deficiencies, as these occur less commonly.34

Vitamins A and K supplementation is based on procedure type34
For most patients, a multivitamin supplement with the daily allowance of fat-soluble vitamins is enough.31

  • Biliopancreatic diversion with duodenal switch
    • Vitamin A: 10,000 IU/day
    • Vitamin K: 300 mcg/day
  • Gastric banding
    • Vitamin A: 5,000 IU/day (weak evidence)
    • Vitamin K: 90 to 120 mcg/day

Vitamin E supplementation

  • There is not strong evidence to support specific doses.34

Folic acid

Reduction in dietary folate intake.

Recommend screening prior to and monitoring all patients after surgery for folate deficiency (e.g., red blood cells, folate, homocysteine, methylmalonic acid [MMA]).34

Recommend a multivitamin supplement with at least 400 mcg to 800 mcg/day.6,23,24,31,34

Recommend 800 mcg/day to 1,000 mcg/day in women of child bearing age.34


Iron is absorbed in first part of the intestines which is bypassed in Roux-en-Y gastric bypass.14

The Roux-en-Y gastric bypass may produce achlorhydria also reducing iron absorption.14

Recommend screening all patients prior to surgery for iron deficiency (e.g., serum iron, transferrin, total iron binding capacity, signs and symptoms of deficiency).34

Recommend monitoring all patients within three months after surgery and at least every three to six months for the first year, annually thereafter.34

  • Monitoring should include a complete blood count, total iron binding capacity, ferritin, soluble transferrin receptor (if available), as well as signs and symptoms.34

Recommend at least 18 mg of elemental iron (often in multivitamin) in low-risk patients (e.g., males, no history of anemia).34

Menstruating females should have at least 45 to 60 mg of elemental iron daily.31,34

Guidelines do not recommend one formulation over another.31

  • Ferrous sulfate may be less well absorbed, especially without an acidic environment.14
  • Consider alternative salts/formulations of iron, if needed.14

Avoid enteric-coated or sustained-release formulations.14,31

Consider parenteral iron, if needed.11,14,15,22,23,25


Reduced dietary intake.

Deficiency can lead to detrimental effects on the heart, gastrointestinal system, and peripheral and central nervous system.

Consider screening patients for deficiency (whole blood).34

Recommending monitoring symptomatic patients and high-risk patients after surgery (e.g., females, patients with heart failure, black patients, refusing to attend nutritional clinic post-op).34

  • Monitor within six months of surgery and then every three to six months until deficiencies resolve.34

Recommend a thiamine-containing multivitamin providing at least 12 mg/day for all patients.34

  • In cases of deficiency, additional thiamine is necessary.15
  • Some recommend at least 50 mg daily to prevent deficiency.34

In patients with intractable vomiting, consider intramuscular thiamine.14,15,22

Vitamin B12

Vitamin B12 absorption is dependent on presence of acid and intrinsic factor (both reduced with Roux-en-Y gastric bypass).14

Vitamin B12 deficiency reported in less than 20% of patients after Roux-en-Y gastric bypass and up to 20% in patients after sleeve gastrectomy.34

Recommend screening all patients for B12 deficiency prior to surgery. Add methylmalonic acid (MMA) as serum B12 levels may not adequately identify deficiencies.34

Recommend monitoring (B12, MMA, with or without homocysteine) with patients after Roux-en-Y gastric bypass, sleeve gastrectomy, and biliopancreatic diversion.34

  • Every three months for the first year, then at least yearly.34

Recommend supplementation for all patients after surgery with oral doses of 350 mcg/day to 500 mcg/day.34

  • Higher doses of oral therapy (e.g., 1,000 mcg daily) may be needed.31
  • If oral therapy is not effective, consider the nasal (weekly) or injectable options (monthly).14,15,22,23,31,34

Zinc and copper

Reduced absorption in some patients.

  • Consider screening patients prior to Roux-en-Y gastric bypass and biliopancreatic diversion surgeries (e.g., zinc, copper, ceruloplasmin).34
    • Serum copper and ceruloplasmin are recommended to assess copper levels, but are acute phase reactants and can also be affected by things such as inflammation, anemia, medications, etc.34
    • Erythrocyte superoxide dismutase may be a better marker for copper deficiency, if available.34
  • Recommend monitoring levels after Roux-en-Y gastric bypass and biliopancreatic diversion surgeries, especially in patients that are symptomatic.34
  • Consider proactive supplementation based on surgery type, or supplement in patients with documented deficiencies.31,34

Zinc supplementation

  • Biliopancreatic diversion: multivitamin with minerals containing 16 to 22 mg/day.
  • Roux-en-Y gastric bypass multivitamin with minerals containing 8 to 22 mg/day.
  • Sleeve gastrectomy/gastric banding: multivitamin with minerals containing 8 to 11 mg/day.
  • Check copper levels in patients receiving zinc supplementation, as this can lead to copper deficiency.31
    • Recommend 1 mg copper for every 8 to 15 mg of zinc to prevent copper deficiency.34

Copper supplementation

  • Recommend copper 1 to 2 mg daily as part of a multivitamin based on surgery type:15,26,34
    • Biliopancreatic diversion or Roux-en Y gastric bypass: 2 mg/day.
    • Sleeve gastrectomy or gastric banding: 1 mg/day

Project Leader in preparation of this clinical resource (340310): Beth Bryant, Pharm.D., BCPS, Assistant Editor


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Cite this document as follows: Clinical Resource, Bariatric Surgery and Medication Use. Pharmacist’s Letter/Prescriber’s Letter. March 2018.

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