Allergy season can be the worst time of year for people suffering with restless legs syndrome because popular over the counter medications can make symptoms much worse, a top expert warns.

“Patients with restless legs syndrome (RLS) already have difficulty sleeping as their symptoms tend to worsen at night or with rest, but sedating antihistamines, such as Benadryl, can intensify the symptoms,” says Dr. William Ondo.

Nearly 12 million Americans have restless legs syndrome, which is considered both a neurological and a sleep disorder as patients feel uncomfortable sensations and strong urges to move their legs, which can sometimes be painful and often disrupts sleep.

But allergies cause problems because many people take sedating and non-sedating antihistamines to help treat the symptoms of seasonal allergies, and this makes their RLS worse, says Dr. Ondo, a neurologist with Houston Methodist Hospital in Houston.   “We don’t yet understand why sedating antihistamines worsen restless legs syndrome, but we do know that non-sedating antihistamines do not affect the symptoms as much because they do not enter the brain as easily,” he adds.

Also, people who assume they are allergic to Benadryl or other sedating antihistamines because it makes them feel hyper should consult a neurologist because they may have undiagnosed RLS, Dr. Ondo recommends.