Precautions and Warnings With Lorcaserin

Specific Lorcaserin Precautions and Warnings

Some warnings and precautions to be aware of prior to taking this drug include the following:
  • Lorcaserin has been reported to cause unusual changes in mood and behavior. These side effects may be more likely to occur with higher-than-recommended doses. Do not take more of this medication than prescribed. Also, let your healthcare provider know if you develop any signs of unusual behavior, such as:
    • Abnormal feelings of happiness (euphoria)
    • Hallucinations (seeing or hearing things that are not real)
    • Feelings of being outside one's body (disassociation).
  • This medication may increase the risk for depression or thoughts of suicide. Please seek immediate medical help if you feel depressed, have thoughts of harming yourself, or develop any other changes in your mood, thoughts, or behavior.
  • Medications that affect serotonin (a brain chemical), including lorcaserin, have the potential to cause a rare but serious reaction known as serotonin syndrome. Many prescription and nonprescription medications affect serotonin (see Drug Interactions With Lorcaserin). Taking lorcaserin with medications that affect dopamine (another brain chemical) may increase your risk for developing similar dangerous symptoms. Contact your healthcare provider immediately if you develop any symptoms of serotonin syndrome, such as:
    • Sweating, a fever, or feeling very hot
    • Muscle stiffness, twitching, or spasms
    • Problems with coordination and walking
    • Confusion or disorientation
    • Restlessness
    • Nausea, vomiting, and diarrhea.
  • This medication may increase the risk for developing heart valve problems. Let your healthcare provider know if you develop symptoms of heart valve disease, such as:
    • Shortness of breath
    • Swelling in the arms, hands, legs, ankles, or feet
    • Dizziness
    • Persistent weakness and fatigue
    • A fast or irregular heartbeat.
  • If you are being treated for diabetes, you may develop low blood sugar levels (hypoglycemia) as you start losing weight from lorcaserin. Your healthcare provider may recommend you monitor your blood sugar levels more closely during lorcaserin treatment. You may need lower doses of your diabetes medications.
  • Lorcaserin may cause a rare but serious medical problem known as priapism (a painful erection lasting for more than four hours). Stop taking lorcaserin and seek immediate medical care if you experience an erection that lasts longer than four hours, even if it is not painful. If not treated immediately, priapism can cause impotency and permanent damage to the penis.
  • In clinical trials, some people experienced a decrease in their heart rate while taking lorcaserin. A heart rate that is too slow can be potentially dangerous. Make sure your healthcare provider knows if you already have a slow heart rate or heart block, or if you feel dizzy or lightheaded during treatment.
  • This medication has been reported to cause a decrease in red blood cells and white blood cells, which could increase the risk for anemia or infections. Your healthcare provider may choose to monitor your blood cell count periodically during treatment.
  • Lorcaserin may increase blood levels of prolactin (a type of hormone). Tell your healthcare provider if you have signs of abnormally elevated prolactin, such as enlarged breasts (especially in men), or breast discharge. He or she can measure your prolactin levels with a simple blood test.
  • Other diet medications have been associated with a rare but serious condition known as pulmonary hypertension. This condition occurs when the blood pressure in the arteries of the lungs becomes too high. This causes the heart to work harder than normal to pump blood.

At this time, it is unknown if lorcaserin also increases the risk for pulmonary hypertension. Let your healthcare provider know if you experience shortness of breath or lightheadedness, especially during physical activity, as this may be a sign of pulmonary hypertension.

  • Lorcaserin has been reported to cause problems with attention and memory. It can also make you feel confused and more tired than usual. These side effects may affect your ability to perform complex tasks that require alertness, such as driving. You should avoid performing activities that require mental or motor concentration, such as driving a car or operating heavy machinery, until you know how this medication affects you.
  • Lorcaserin is a pregnancy Category X medication. This means it should not be used during pregnancy (see Belviq and Pregnancy for more information).
  • It is unknown if lorcaserin passes through breast milk. Therefore, if you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking the drug (see Belviq and Breastfeeding).
Last reviewed by: Kristi Monson, PharmD
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