If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669. Symptoms of overdose may include: chest pain, fast/pounding/irregular heartbeat, headache, shaking (tremors), nervousness, weakness, severe dizziness, seizures.