Research suggests that the seizure drug Dilantin may be linked to brain damage— specifically that its use may negatively affect the cerebellum, the brain’s movement center.

The cerebellum controls voluntary movement, including speech, motor skills, and walking. When a person’s cerebellum is damaged, their ability to speak clearly, move smoothly, or walk steadily may be affected.

Damage to the cerebellum is called cerebellar atrophy or cerebellar degeneration. In severe cases, the cerebellum can become so damaged that it actually shrinks. In cases of cerebellar atrophy or degeneration, connections between the neurons become impeded, inhibiting the brain’s ability to send messages.

A peer-reviewed neurological journal published the case study of a 20-year-old woman who suffered focal cerebral atrophy and other neurological problems as a result of taking Dilantin (phenytoin). Researchers classified the woman’s condition as acute phenytoin/Dilantin intoxication.

According to the publication, the woman came under physicians’ care due to neurological problems as a result of a brain injury. Her doctors prescribed Dilantin as a preventative in the event she developed seizures.

However, she suffered a variety of neurological issues, including problems with muscle control — specifically a limp — facial tremors, involuntary eye movements, involuntary movements in her tongue, and slurred speech. The woman’s cognitive abilities were also impacted. Researchers documented a shortened attention span, inappropriate laughter, and “childish behavior.”

According to the case study, Dilantin is known to have such side effects, but they are usually reversible. Since the patient was given Dilantin as a preventative for seizures which never manifested, doctors quickly tapered off her dose. But some of the side effects researchers suspected were caused by Dilantin persisted.

A follow-up six months later showed many of the same Dilantin side effects. The woman’s condition had improved and she reported feeling less sleepy, but some of her cognitive and movement problems remained, including issues with memory and abstract thinking.

A brain scan showed her skull had thickened and parts of her brain shrunk, a condition known as focal cerebral atrophy or cerebellar atrophy.

The scans also revealed that parts of her brain had hypometabolism. This means that the tissue was not working as much as it does in a healthy person, using less oxygen and nutrients.

Dilantin Side Effects

Researchers noted that patients’ susceptibility to Dilantin side effects varies greatly. Though they described the 20-year-old woman’s case as “unusual,” the authors pointed out that predicting Dilantin’s side effects is difficult.

For example, the case report says the amount of Dilantin in blood serum does not correlate with developing focal cerebral atrophy, however, blood serum levels are linked to other side effects of the drug.

Each individual’s metabolism may affect the amount of Dilantin that remains in the body, which in turn can lead to a potentially toxic buildup of the drug, according to the study.

Dilantin/phenytoin side effects often manifest as neurological problems in the form of sleepiness, twitching, and difficulty moving.

Though Dilantin side effects are usually reversible, stopping seizure medication is a complicated affair and can lead to rebound seizures, complicating the process of weaning off the medication.

Even with the risk of side effects, Dilantin is still commonly prescribed due to its ability to control seizures, which could be life-threatening. The World Health Organization includes the drug on its List of Essential Medicines, which the organization describes as drugs that are needed to support a basic health system.

More research is needed to clarify the possible connectionbetween Dilantin and damage to the cerebellum, according to the Journal of Epilepsy Research.