In higher doses, the drug causes respiratory depression and decreases the activity of the GI tract. High doses increase blood pressure and can cause hallucinations, nightmares, dysphoria, tachycardia, and dizziness. The latter properties have led to its decreased use. In angina, pentazocine increases the mean aortic pressure and pulmonary arterial pressure and, thus, increases the work of the heart. The drug decreases renal plasma flow. Despite its antagonist action, pentazocine does not antagonize the respiratory depression of morphine, but it can precipitate a withdrawal syndrome in a morphine abuser. Tolerance and dependence develop on repeated use.