Adverse reactions of orphenadrine are mainly due to the mild anti-cholinergic action of orphenadrine, and are usually associated with higher dosage. Dryness of the mouth is usually the first adverse effect to appear. When the daily dose is increased, possible adverse effects include: tachycardia , palpitation, urinary hesitancy or retention, blurred vision , dilatation of pupils, increased ocular tension , weakness, nausea , vomiting, headache, dizziness, constipation, drowsiness, hypersensitivity reactions, pruritus , hallucinations, agitation, tremor , gastric irritation, and rarely urticaria and other dermatoses. Infrequently, an elderly patient may experience some degree of mental confusion. These adverse reactions can usually be eliminated by reduction in dosage. Very rare cases of aplastic anemia associated with the use of orphenadrine tablets have been reported. No causal relationship has been established.
Some patients who take alpha-blocker therapy for the treatment of high blood pressure or prostate enlargement may experience dizziness or light-headedness which may be caused by low blood pressure upon sitting or standing up quickly. Certain patients have experienced these symptoms when taking sildenafil with alpha-blockers. This is most likely to happen within 4 hours after taking sildenafil. In order to reduce the chance that these symptoms might happen, you should be on a regular daily dose of your alpha-blocker before you start sildenafil. Your doctor may start you on a lower dose (25mg) of sildenafil.