Tonic-clonic Seizure
1 medicine
A tonic-clonic seizure causes sudden loss of consciousness, full-body stiffening and rhythmic jerking. After a second unprovoked seizure, long-term anticonvulsant treatment reduces recurrence.
Key facts
- A tonic-clonic seizure is the classic convulsive episode: a tonic phase of muscle stiffening and lost consciousness, then a clonic phase of rhythmic jerking lasting one to three minutes.
- Afterwards, the person is usually confused, exhausted or drowsy for up to an hour.
- After more than one unprovoked seizure, most neurologists start an anticonvulsant such as phenytoin, which stabilises sodium channels in nerve membranes; see the neurology category for the broader picture.
- A seizure lasting more than five minutes, or repeated seizures without regaining consciousness, is a medical emergency.
Managing tonic-clonic seizures long-term
The aim of treatment is to suppress abnormal electrical firing in the brain enough to prevent further episodes. Phenytoin is one of the older, well-studied anticonvulsants used for this, working by stabilising voltage-gated sodium channels in nerve membranes, and it is used both in acute settings and for longer-term control in people who tolerate it well. For a broader view of conditions and medicines in this field, see the neurology category.
When to seek help
Call emergency services if a seizure lasts more than five minutes, if seizures repeat without the person regaining consciousness, or for a first-ever seizure. Ongoing epilepsy care is specialist-led.
This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.