According to MedLine both drugs have basically the same side-effect profile. Weight gain is not a side-effect; in fact, the opposite [weight loss] seems to be the rule with SSRIs.
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[This is a cut & paste from the MedLine article.]
Check with your doctor as soon as possible if any of the following side effects occur:
Less common or rare
Breast tenderness or enlargement; fast or irregular heartbeat; fast talking and excited feelings or actions that are out of control; fever ; inability to sit still; low blood sodium (confusion, convulsions [seizures], drowsiness, dryness of mouth, increased thirst, lack of energy); nose bleeds ; red or purple spots on skin; restlessness; serotonin syndrome (diarrhea, fever, increased sweating, mood or behavior changes, overactive reflexes, racing heartbeat, restlessness, shivering or shaking); skin rash, hives, or itching; unusual or sudden body or facial movements or postures; unusual secretion of milk (in females)
Zoloft: [url="http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202651.html"]http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202651.html[/url]
Celexa: [url="http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/203653.html"]http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/203653.html[/url]
NOTE:
Both warn of "Serotonin Syndrome" - a rare and serious side-effect.
Here's the link for serum serotonin levels: [url="http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm"]http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm[/url]
Here's the link for serotonin uptake: [url="http://www.nlm.nih.gov/medlineplus/ency/imagepage/9877.htm"]http://www.nlm.nih.gov/medlineplus/ency/imagepage/9877.htm[/url]