Propranolol is a nonselective beta-adrenergic blocker with a usual starting dose of 40 mg a day. This is gradually increased to a total of 240 mg a day taken in divided doses. A long-acting form is available with a dose range of 60–160 mg once a day. Patients with coexistent hypertension, anxiety, mitral valve prolapse, or benign essential tremor could benefit from its use. Common side-effects are depression, bradyarrhythmia, fatigue, and exercise intolerance. Myasthenia gravis and diabetes are relative contra-indications. Contra-indications include asthma, congestive heart failure, AV block, and severe sinus bradycardia. For more you can view this article. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2671824/

MECHANISM OF ACTION

The possible mechanisms of action of propranolol in the prophylactic treatment of migraine are listed below:

Blockade of these beta adrenergic receptors results in inhibition of arterial dilatation.

The drug may block the sticky elements of the blood, the platelets, from adhering together and thus releasing substances which cause blood vessels to constrict and dilate.

There may be a central mechanism of action in the brain "turning off" the generators that cause migraine.

There is a general presumption that the effect must be related to the direct effect on blood vessels, but there is a slight weakness in this view, because other beta blockers do not seem to be as effective in migraines.

I suspect that central effects are more important. A common side effect of propranolol is tiredness (like with amitryptiline). Perhaps the effect is more related to the changed balance of central excitatory and inhibitory neurotransmitters reducing the likelihood of the "migraine mechanism" described by Drs Lane & Davies in 'Migraine' from kicking in. (I would well recommend this book - it has been an inspiration in my understanding of headache)

Even in its chronic phase migraine generally has a cyclical element even if the patient never has symptom-free days. The distinction between episodic and chronic migraine in the IHS classification is one of definition

PS it is easy to confuse the a true constant daily headache with the post-ictal headache that extends after a migraine. A clue is whether they have symptom-free days. Another is whether the interictal headache is varies in intensity.

Some people appear to have migraines that overlay a constant daily headache

Moreover, Beta blocker• Clinical findings support the efficacy of propranolol, Exhibit high affinity for 5-HT receptor( 1a, 1b/d,2a)• propranolol blocked CSD in rats, without altering regional cerebral blood flow and systemic arterial blood pressure

The right answer to tis question is: we still don't know ! Efficacy of this drug was obserwed in patients treated due to cardiovascular illnesess. A hypothetical mechanism of action of propranolol in prophylaxis of migreine are posted above.

Although the usual hocus pocus, no one really knows how these traditional agents work. However, we may think about the possibility of acting on pre-junctional Beta receptors, therefore reducing firing rate at the locus ceruleus and reducing the nor-adrenaline synthesis thru the inhibition of the tirosine hydroxilase. In addition, downregulating the 5-HT2b and 2c receptores. Nevertheless, just guessing and serendipity.... Yours