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Belviq XR Side Effects

Generic name: lorcaserin

Medically reviewed by Last updated on May 3, 2020.

Note: This document contains side effect information about lorcaserin. Some of the dosage forms listed on this page may not apply to the brand name Belviq XR.

For the Consumer

Applies to lorcaserin: oral tablet, oral tablet extended release

Side effects requiring immediate medical attention

Along with its needed effects, lorcaserin (the active ingredient contained in Belviq XR) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking lorcaserin:

More common

  • Anxiety
  • bladder pain
  • bloody or cloudy urine
  • blurred vision
  • body aches or pain
  • chills
  • cold sweats
  • coma
  • confusion
  • cool, pale skin
  • cough
  • depression
  • difficult, burning, or painful urination
  • difficulty with breathing
  • dizziness
  • ear congestion
  • fast heartbeat
  • fever
  • frequent urge to urinate
  • headache
  • increased hunger
  • loss of voice
  • lower back or side pain
  • nasal congestion
  • nausea
  • nightmares
  • pounding in the ears
  • runny nose
  • seizures
  • shakiness
  • slow or fast heartbeat
  • slurred speech
  • sneezing
  • sore throat
  • swelling of the breasts or breast soreness in both females and males
  • unexpected or excess milk flow from the breasts
  • unusual tiredness or weakness

Less common

  • Bloating or swelling of the face, arms, hands, lower legs, or feet
  • decreased ability to exercise
  • dry mouth
  • flushed, dry skin
  • fruit-like breath odor
  • increased hunger
  • increased sensitivity to sunlight
  • increased thirst
  • increased urination
  • itching, pain, redness, or swelling of the eye or eyelid
  • joint pain
  • loss of consciousness
  • rapid weight gain
  • severe skin rash or hives
  • stomachache
  • sweating
  • swollen glands
  • tingling of the hands or feet
  • trouble with breathing
  • trouble with sleeping
  • unexplained weight loss
  • unusual weight gain or loss
  • vomiting
  • watering of the eyes


  • Black, tarry, stools
  • chest pain
  • cough or hoarseness
  • pale skin
  • sores, ulcers, or white spots on the lips or in the mouth
  • swollen glands
  • unusual bleeding or bruising

Incidence not known

  • Agitation
  • confusion
  • convulsions
  • diarrhea
  • high fever
  • increased sweating
  • loss of bladder control
  • overactive reflexes
  • painful or prolonged erection of the penis
  • poor coordination
  • restlessness
  • severe muscle stiffness
  • shivering
  • talking or acting with excitement you cannot control
  • trembling or shaking
  • twitching
  • unusually pale skin

Get emergency help immediately if any of the following symptoms of overdose occur while taking lorcaserin:

Symptoms of overdose

  • Abdominal or stomach discomfort
  • false or unusual sense of well-being
  • seeing, hearing, or feeling things that are not there

Side effects not requiring immediate medical attention

Some side effects of lorcaserin may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Back pain
  • difficulty having a bowel movement (stool)
  • muscle aches

Less common

  • Decreased appetite
  • difficulty with concentration
  • dry eyes
  • muscle spasms
  • muscle, joint, or bone pain
  • problems with memory
  • rash
  • sleeplessness
  • stress
  • toothache
  • trouble seeing

For Healthcare Professionals

Applies to lorcaserin: oral tablet, oral tablet extended release

Nervous system

Very common (10% or more): Headache (up to 16.8%)

Common (1% to 10%): Dizziness, impaired attention/memory

Uncommon (0.1% to 1%): Tremor, confusion, disorientation

Very rare (less than 0.01%): Serotonergic excess

Frequency not reported: Neuroleptic Malignant Syndrome/serotonin syndrome, somnolence[Ref]


Common (1% to 10%): Hypertension

Uncommon (0.1% to 1%): Regurgitant cardiac valvular heart disease, bradycardia[Ref]


Common (1% to 10%): Anxiety, insomnia, stress, depression/mood problems

Uncommon (0.1% to 1%): Euphoria, suicidal ideation

Frequency not reported: Hallucination, dissociation[Ref]


Very common (10% or more): Decreased lymphocyte count (up to 12.2%), decreased hemoglobin (up to 10.4%)

Common (1% to 10%): Decreased red blood cell count, decreased neutrophil count

Uncommon (0.1% to 1%): Decreased white blood cell count[Ref]


Very common (10% or more): Hypoglycemia (up to 29.3%)

Common (1% to 10%): Worsening of diabetes mellitus, elevated prolactin[Ref]


Very common (10% or more): Upper respiratory tract infection (up to 13.7%), nasopharyngitis (up to 13%)

Common (1% to 10%): Cough, oropharyngeal pain, sinus congestion[Ref]


Common (1% to 10%): Fatigue, peripheral edema, chills[Ref]


The most common adverse reactions for non-diabetic patients were headache, dizziness, fatigue, nausea, dry mouth, and constipation. For diabetic patients, the most common adverse reactions were hypoglycemia, headache, back pain, cough, and fatigue.[Ref]


Common (1% to 10%): Rash

Uncommon (0.1% to 1%): Hyperhidrosis[Ref]


Common (1% to 10%): Nausea, diarrhea, constipation, dry mouth, vomiting, toothache, gastroenteritis[Ref]


Common (1% to 10%): Urinary tract infection[Ref]


Common (1% to 10%): Seasonal allergy[Ref]


Common (1% to 10%): Decreased appetite[Ref]


Very common (10% or more): Back pain (up to 11.7%)

Common (1% to 10%): Musculoskeletal pain, muscle spasms[Ref]


Non-diabetic patients experienced events of blurred vision, dry eye, and visual impairment. Diabetic patients experienced visual disorders, conjunctival infections, irritations and inflammations, ocular sensation disorders, and cataract conditions.[Ref]

Common (1% to 10%): Eye disorder[Ref]


Frequency not reported: Increased incidence of cancer[Ref]

The U.S. Food and Drug Administration (FDA) reports that safety data from a lorcaserin clinical trial shows a possible increased risk of cancer. In this trial of 12,000 participants over 5 years, more patients taking lorcaserin were diagnosed with cancer compared to patients taking placebo. The cause of the cancer is uncertain, and it is unknown if this drug contributed to the cancer risk. The FDA will continue to evaluate the clinical trial results and communicate final conclusions and recommendations once the review is complete.[Ref]


1. "Product Information. Belviq (lorcaserin)." Eisai Inc, Teaneck, NJ.

2. US Food and Drug Administration "Safety clinical trial shows possible increased risk of cancer with weightloss medicine Belviq, Belviq XR (lorcaserin) Available from: URL:" ([2020, Jan 14]):

More about Belviq XR (lorcaserin)

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.