Tagamet is available over the counter without prescription for complaints of heartburn and GI distress. However, due to a drug-drug interaction where Tagamet causes an increase in the blood level of paroxetine and in some patients this can be as much as 50% to 80%, caution is advised. An increased chance of side effects from paroxetine due to higher levels or possible toxicity can occur. Side effects might present as dizziness, headache, nausea, and sedation.