Treatment with Belviq may cause serious side effects, including serotonin syndrome, particularly when taken with certain medicines that increase serotonin levels or activate serotonin receptors.

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"It isn't a huge surprise when you consider many positive effects exercise can have with regards to the brain chemistry: dopamine, serotonin, endorphin, epinephrine -- these are all associated with mood altering effects, " said Dr. Cedric Bryant, the chief science officer for the American Council on Exercise.

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New drugs that work more directly to nourish neurons could be more effective than existing serotonin-based remedies, have fewer side effects or kick in slightly faster.

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These suggest that although serotonin may be central to Ecstasy's long-term effects, other neurotransmitters could be involved as well.

ECONOMIST: Recreational drugs

The current crop of drugs, including the big names such as Prozac, Celexa and Effexor, work by boosting levels of brain transmitters serotonin or norepinephrine or both, but they take several weeks to kick in and have side effects including sexual dysfunction.

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