The most common side effects related to Phenos in children are jerky movements of the eyes (nystagmus) and overgrowth of the gums. In some children, Phenos causes problems with thinking or behavior, mood change, slow or clumsy movements, or a loss of energy. Other side effects from high doses include unsteadiness in the feet and hands, sleepiness, and vomiting. These may be avoidable if the dose is increased slowly. These side effects quickly disappear when the dose is reduced.

Phenos has not been reported to cause weight gain. However, weight loss can occur with longer term use of a higher dose of Phenos. Please consult your doctor if you experience weight gain after taking Phenos.

Suddenly stopping Phenos may cause non-stop seizures (called status epilepticus), which can endanger life. Do not stop taking the medicine without consulting your doctor. If required, your doctor will slowly reduce the dose before stopping it completely.

Phenos does affect birth control. Phenos can decrease the effect of oral contraceptives (birth control pills) which can make the contraceptive (birth control) effect unreliable. Please talk to your doctor if you are asked to take the two medicines together as you may need to use extra protection for birth control.

Phenos can make you feel sleepy (sedation, somnolence, and drowsiness). Please consult your doctor if you feel very sleepy after taking Phenos, especially during the first few weeks of treatment or following a dose increase. Talk to your doctor as you may be advised not to drive or use machines until it is established that your ability to perform such activities is not affected.

Overdose of Phenos may cause jerky movements of the eyes (nystagmus), unclear speech, loss of balance, tremor, muscle stiffness or weakness, nausea, vomiting, lightheadedness, fainting, blurred vision, slow and shallow breathing and even coma. Phenos overdose can cause very low blood pressure and respiratory problems. As a result of this, the patient can even die.

On an average, Phenos may stay in your system for 5-6 days. This duration varies from person to person. In some cases, it may stay for about 9-10 days.

You should not take Phenos if you have liver disease, especially if you have a history of developing a liver problem due to Phenos. Also, patients taking Delavirdine (a medicine used in the treatment of HIV infection) should not take Phenos. Phenos may reduce the effectiveness of Delavirdine on HIV and the virus may also become resistant to Delavirdine. It is advised that you inform your doctor if you have any existing heart disorder before you receive Phenos.

Phenos can be taken with ibuprofen. No drug-drug interactions have been reported between the two. However, interactions can occur. Please consult your doctor before taking the two medicines together.