Acute toxic effects are usually extensions of the therapeutic actions of the drug and are most often due to overdosage. Excessive doses may cause a sharp rise in blood pressure sufficient to produce cerebral hemorrhage. Other effects (usually transient) include headache, restlessness, anxiety, tension, tremor, weakness, dizziness, confusion, delirium hallucinations, pallor, respiratory difficulty, palpitation, sweating, nausea or vomiting. Repeated injections may cause contraction of the bladder sphincter and interfere with voluntary urination. The possibility of urinary retention, especially in the elderly male, should be kept in mind.