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Lorcaserin (By mouth)

Lorcaserin (lor-KA-ser-in)

Used in combination with diet and exercise to help you reach and maintain a healthy weight.

Brand Name(s):


There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

Do not use this medicine if you have had an allergic reaction to lorcaserin, or if you are pregnant.

How to Use This Medicine:


  • Your doctor will tell you how much medicine to use. Do not use more than directed.
  • Carefully follow your doctor's instructions for a reduced-calorie diet plan and regular exercise. Talk with your doctor before starting any exercise program.
  • Stop taking this medicine if you do not lose 5% of your weight within the first 12 weeks of treatment.
  • Read and follow the patient instructions that come with this medicine. Talk to your doctor or pharmacist if you have any questions.

If a dose is missed:

  • Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

How to Store and Dispose of This Medicine:

  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.
  • Ask your pharmacist, doctor, or health caregiver about the best way to dispose of any outdated medicine or medicine no longer needed.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Make sure your doctor knows if you are also using St John's wort, cabergoline (Dostinex®), dextromethorphan (Benylin®, Robitussin DM®), linezolid (Zyvox®), lithium (Eskalith®, Lithobid®), tramadol (Ultram®), tryptophan, medicine to treat depression (such as amitriptyline, bupropion, citalopram, fluoxetine, nortriptyline, sertraline, Cymbalta®, Effexor®, Elavil®, Lexapro®, Pristiq®, Wellbutrin®), an MAO inhibitor (such as Eldepryl®, Marplan®, Nardil®, Parnate®), medicine to treat migraine headache (such as sumatriptan, Frova®, Maxalt®, Relpax®, Zomig®), any medicine to treat mental illness, or a phenothiazine medicine (such as promethazine, Phenergan®, Thorazine®).
  • Tell your doctor if you are also using insulin or diabetes medicine that you take by mouth (such as glimepiride, glipizide, glyburide, Amaryl®), medicine for erectile dysfunction (such as sildenafil, tadalafil, vardenafil, Cialis®, Levitra®, Viagra®), or any other medicine to help you lose weight (such as phentermine, Suprenza™).

Warnings While Using This Medicine:

  • It is not safe to take this medicine during pregnancy. It could harm an unborn baby. Tell your doctor right away if you become pregnant.
  • Make sure your doctor knows if you are breastfeeding, or if you have kidney or liver disease, depression, diabetes, high prolactin in the blood, or mental illness. Tell your doctor if you have a blood disorder, such as leukemia, multiple myeloma, or sickle cell anemia.
  • Tell your doctor if you have a heart problem, such as congestive heart failure, heart valve disease, heart block, or a slow heartbeat.
  • This medicine may cause serious conditions, such as serotonin syndrome or neuroleptic malignant syndrome (NMS), when taken with certain medicines. Call your doctor right away if you have anxiety, restlessness, fast heartbeat, fever, sweating, muscle spasms, twitching, nausea, vomiting, diarrhea, or seeing or hearing things that are not there.
  • Tell your doctor if you have erectile dysfunction, a penis with an abnormal shape, or if you have ever had a prolonged erection. This medicine may cause you to have an erection that lasts longer than 4 hours. Stop taking this medicine and call your doctor right away, or go to the emergency room if this happens.
  • Tell your doctor right away if you have rapid weight gain, swelling of the ankles, feet, or lower legs, or trouble breathing. These could be symptoms of a heart problem.
  • This medicine may make you dizzy or drowsy. Avoid driving, using machines, or doing anything else that could be dangerous until you know how this medicine affects you.
  • Tell your doctor if you have any strange thoughts or behavior while you are taking this medicine, such as confusion, worsened depression, hallucinations (seeing, hearing, or feeling things that are not there), suicidal thoughts, or unusual excitement, nervousness, or anger.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
  • Diabetes patients: This medicine may achieve weight loss, which could improve your diabetes. However, weight loss may also increase your risk of hypoglycemia (low blood sugar). Check your blood sugar more often, both before and during treatment with this medicine. Tell your doctor if you notice any changes in your blood sugar levels.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Agitation, confusion, memory loss, restlessness
  • Anxiety, restlessness, fast heartbeat, fever, sweating, muscle spasms, twitching, nausea, vomiting, diarrhea, seeing or hearing things that are not there
  • Dizziness, tiredness, headache, weakness, faint
  • Fast, slow, or uneven heartbeat
  • Fever, sweating, confusion, uneven heartbeat, muscle stiffness
  • Painful or prolonged erection of the penis that lasts longer than 4 hours
  • Rapid weight gain, swelling of the ankles, feet, or lower legs
  • Trouble breathing
  • Unusual bleeding, bruising, or weakness
  • Unusual mood or behavior, extreme good mood

If you notice these less serious side effects, talk with your doctor:

  • Back pain
  • Cough
  • Dry mouth
  • Headache
  • Swelling of the breasts or milky discharge from breasts
  • Tiredness

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 5/1/2020

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