New studies suggest that many of the available antiepileptic drugs, especially the older ones, can have other negative effects besides worsening seizures. A range of epilepsy drugs can cause serious skin disorders, such as the potentially fatal Stevens-Johnson syndrome and toxic epidermal necrolysis (severe skin loss due to skin cell death). Short-term skin disorders have been reported in as many as 21 per cent of those taking older drugs such as phenobarbital, phenytoin, carbamazepine, valproic acid and lamotrigine (Lancet, 1999; 353: 2190-4). In addition, the antiepileptic drug vigabatrin caused vision problems in 73 per cent of participants in one small British study (BMJ, 1998; 317: 206).

But most disturbing are the other adverse effects on the brain, including a decline in mental function and memory. Although these effects are usually modest, they can be clinically significant for some patients (Epilepsia, 1986; 27: 760-8).

Phenobarbital appears to produce the most reports of mental dysfunction (Neurology, 1995; 45: 1494-9), but drugs like carbamazepine, phenytoin, valproate and benzodiazepines can also have this effect (Epilepsia, 1999; 40: 1279-85).

Recently, researchers have turned their attention to the possible effects of a newer drug, topiramate, on cognition and memory. In one trial, it induced a drop of almost 50 per cent in word-learning performance (Neurology, 1999; 52: 321-7). Other studies of topiramate in patients with epilepsy have shown similar, more modest, but nevertheless significant, effects (Epilepsia, 1998; 39 [Suppl 6]: 188-9; Epilepsia, 2001; 42 [Suppl 2]: 75).

Some doctors reason that the trade off is a fair one - control of seizures for a small loss of memory. But what constitutes a small loss for one person may be intolerable for another. For some patients, putting up with the occasional seizure is preferable to purchasing seizure freedom at the price of mental slowing.