In those with fewer than three of these symptoms, the probability is 17%. Classification
Migraine was first comprehensively classified in 1988. The International Headache Society updated their classification of headaches in 2004. A third version was published in 2018. According to this classification, migraine is a primary headache disorder along with tension-type headaches and cluster headaches, among others.Migraine is divided into seven subclasses (some of which include further subdivisions):

Migraine without aura, or "common migraine", involves migraine headaches that are not accompanied by aura. Migraine with aura, or "classic migraine", usually involves migraine headaches accompanied by aura. Less commonly, aura can occur without a headache, or with a nonmigraine headache. Two other varieties are familial hemiplegic migraine and sporadic hemiplegic migraine, in which a person has migraine with aura and with accompanying motor weakness. If a close relative has had the same condition, it is called "familial", otherwise it is called "sporadic". Another variety is basilar-type migraine, where a headache and aura are accompanied by difficulty speaking, world spinning, ringing in ears, or a number of other brainstem-related symptoms, but not motor weakness. This type was initially believed to be due to spasms of the basilar artery, the artery that supplies the brainstem. Now that this mechanism is not believed to be primary, the symptomatic term migraine with brainstem aura (MBA) is preferred. Childhood periodic syndromes that are commonly precursors of migraine include cyclical vomiting (occasional intense periods of vomiting), abdominal migraine (abdominal pain, usually accompanied by nausea), and benign paroxysmal vertigo of childhood (occasional attacks of vertigo).
Because this enzyme system is regarded as the acid (proton, or H+) pump within the gastric mucosa, omeprazole inhibits the final step of acid production.Omeprazole also inhibits both basal and stimulated acid secretion irrespective of the stimulus as it blocks the last step in acid secretion. The drug binds non-competitively so it has a dose-dependent effect.The inhibitory effect of omeprazole occurs within 1 hour after oral administration. The maximum effect occurs within 2 hours. The duration of inhibition is up to 72 hours. When omeprazole is stopped, baseline stomach acid secretory activity returns after 3 to 5 days. The inhibitory effect of omeprazole on acid secretion will plateau after 4 days of repeated daily dosing. Pharmacokinetics
The absorption of omeprazole takes place in the small intestine and is usually completed within 3 to 6 hours. The systemic bioavailability of omeprazole after repeated doses is about 60%. Omeprazole has a volume of distribution of 0.4 L/kg. It has high plasma protein binding of 95%.Omeprazole, as well as other PPIs, are only effective on active H+/K+-ATPase pumps. These pumps are stimulated in the presence of food to aid in digestion. For this reason, patients should be advised to take omeprazole with a glass of water on an empty stomach.