Thanks Harry, these are exactly the clarifications I was looking for.
From LEF: There are two safe forms of niacin:
Immediate-release/crystalline niacin is available as a nutritional supplement and is inexpensive and effective. The niacin in each table is released immediately and usually provokes a “hot flush,” a warm, itchy feeling of the skin. For this reason, starting at small doses, such as 250 mg, can be helpful. The dose can be increased gradually (by 250 mg every four weeks) to achieve the desired amount. Doses greater than 500 mg per day should be used only under medical supervision. Some people take their niacin in small doses, three or four times daily, to spread out the dose. This could be unsafe, and I recommend that patients never take immediate-release niacin more than twice a day.
Extended-release niacin is a time-release preparation, but does not act as slowly as slow-release niacin. This makes it safer than the slow-release preparations that can cause liver side effects. Extended-release niacin also provokes fewer hot flushes than immediate-release niacin. An example is Slo-Niacin®, which is sold over the counter. Niaspan® is an extended-release niacin preparation sold as a prescription drug.
By contrast, slow-release niacin preparations reduce the hot-flush effect by releasing niacin over an extended period of 12 hours or longer. Most of these preparations are unsafe and I do not recommend them. “No-flush” niacin preparations, such as inositol hexaniacinate and nicotinamide, are widely sold as niacin alternatives that do not cause hot flushes. In my experience, however, they simply do not work. In other words, no flush, no effect.
The correct dose of niacin depends on what abnormality you and your doctor are trying to correct. To raise HDL and correct small LDL, a dose of 750-1000 mg a day usually provides full benefit. Increasing this dose to 1500 mg a day may provide slightly greater benefit. To reduce LDL or Lp(a), higher doses (from 1000 mg up to 4000-5000 mg per day) are often used, with higher doses providing greater effects. However, doses this high should be taken only with a physician’s supervision. Keep in mind that it may take three months or longer to realize the full lipid-optimizing benefits of niacin.