Lorcaserin Side Effects

Medically reviewed by Drugs.com. Last updated on Jun 24, 2025.

Applies to lorcaserin: oral tablet.

Serious side effects of lorcaserin

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
• Signs of high blood pressure like very bad headache or dizziness, passing out, or change in eyesight.
• New or worse behavior or mood changes like depression or thoughts of suicide.
• Hallucinations (seeing or hearing things that are not there).
• Slow heartbeat.
• Feeling confused.
• Memory problems or loss.
• Not able to focus.
• Pain when passing urine.
• Passing urine more often.
• Nipple discharge.
• For males, enlarged breasts.
• A severe and sometimes deadly problem called serotonin syndrome may happen. The risk may be greater if you also take certain other drugs. Call your doctor right away if you have agitation; change in balance; confusion; hallucinations; fever; fast or abnormal heartbeat; flushing; muscle twitching or stiffness; seizures; shivering or shaking; sweating a lot; severe diarrhea, upset stomach, or throwing up; or very bad headache.
• A very bad and sometimes deadly health problem called neuroleptic malignant syndrome (NMS) may happen. Call your doctor right away if you have any fever, muscle cramps or stiffness, dizziness, very bad headache, confusion, change in thinking, fast heartbeat, heartbeat that does not feel normal, or are sweating a lot.

Other side effects of lorcaserin

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Headache.
• Feeling dizzy, sleepy, tired, or weak.
• Upset stomach.
• Dry mouth.
• Diarrhea or constipation.
• Cough.
• Back pain.
• Signs of a common cold.
• Nose or throat irritation.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

See also:

For healthcare professionals

Applies to lorcaserin: oral tablet, oral tablet extended release.

General adverse events

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]

Cardiovascular

• Common (1% to 10%): Hypertension
• Uncommon (0.1% to 1%): Regurgitant cardiac valvular heart disease, bradycardia^[Ref]

Psychiatric

• Common (1% to 10%): Anxiety, insomnia, stress, depression/mood problems
• Uncommon (0.1% to 1%): Euphoria, suicidal ideation
• Frequency not reported: Hallucination, dissociation^[Ref]

Hematologic

• 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]

Endocrine

• Very common (10% or more): Hypoglycemia (up to 29.3%)
• Common (1% to 10%): Worsening of diabetes mellitus, elevated prolactin^[Ref]

Respiratory

• 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]

Other

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

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]

Dermatologic

• Common (1% to 10%): Rash
• Uncommon (0.1% to 1%): Hyperhidrosis^[Ref]

Gastrointestinal

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

Genitourinary

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

Immunologic

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

Metabolic

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

Musculoskeletal

• Very common (10% or more): Back pain (up to 11.7%)
• Common (1% to 10%): Musculoskeletal pain, muscle spasms^[Ref]

Ocular

• Common (1% to 10%): Eye disorder^[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]

Oncologic

• 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]

Further information

Lorcaserin side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer