These can be minimized by initiating therapy at low dosages, increasing dosage gradually, and avoiding administration on an empty stomach.The acute adverse effects of high-dose niacin therapy (1–3 grams per day) – which is commonly used in the treatment of hyperlipidemias – can further include hypotension, fatigue, glucose intolerance and insulin resistance, heartburn, blurred or impaired vision, and macular edema. With long-term use, the adverse effects of high-dose niacin therapy (750 mg per day) also include liver failure (associated with fatigue, nausea, and loss of appetite), hepatitis, and acute liver failure; these hepatotoxic effects of niacin occur more often when extended-release dosage forms are used. The long-term use of niacin at greater than or equal to 2 grams per day also significantly increases the risk of cerebral hemorrhage, ischemic stroke, gastrointestinal ulceration and bleeding, diabetes, dyspepsia, and diarrhea. Flushing
Flushing – a short-term dilatation of skin arterioles, causing reddish skin color – usually lasts for about 15 to 30 minutes, although sometimes can persist for weeks. Typically, the face is affected, but the reaction can extend to neck and upper chest. The cause is blood vessel dilation due to elevation in prostaglandin GD2 (PGD2) and serotonin. Flushing was often thought to involve histamine, but histamine has been shown not to be involved in the reaction. Flushing is sometimes accompanied by a prickly or itching sensation, in particular, in areas covered by clothing.Prevention of flushing requires altering or blocking the prostaglandin-mediated pathway. Aspirin taken half an hour before the niacin prevents flushing, as does ibuprofen.
Metirosine (INN and BAN; α-Methyltyrosine, Metyrosine USAN, AMPT) is an antihypertensive drug. It inhibits the enzyme tyrosine hydroxylase and, therefore, catecholamine synthesis, which, as a consequence, depletes the levels of the catecholamines dopamine, adrenaline and noradrenaline in the body. It is available as a generic medication. Clinical use
Metirosine has been shown to suppress catecholamine synthesis and alleviate symptoms related to catecholamine excess, including hypertension, headache, tachycardia, constipation, and tremor. Metirosine is primarily used to reduce these symptoms in patients with pheochromocytoma. It is contraindicated for the treatment of essential hypertension. Metirosine is used as an off-label treatment for DiGeorge syndrome.Metirosine is used in scientific research to investigate the effects of catecholamine depletion on behavior. There is evidence that catecholamine depletion causes an increase in sleepiness that is more pronounced than sleep deprivation, and that the fatigue lingers after the drug is discontinued. Negative mood is also a reported side effect of catecholamine depletion, although this is reported less consistently than sleepiness. See also
p-Chlorophenylalanine

References
External links
"Metyrosine". Drug Information Portal. U.S. National Library of Medicine.