The ADHD stimulant Adderall (amphetamine / dextroamphetamine) has been reported to cause both diarrhea and constipation as a side effect. A laxative effect appears to be more common than constipation, but this may vary among patients. In studies, at least 5% of patients (5 out of every 100) reported having diarrhea as a side effect with Adderall. More @Wikipedia
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