Niacin eliminates ED, arthritis and improves cholesterol and much much more.
Niacin is probably the most underappreciated vitamin. I read a book on Niacin (Drs Hoffer and Saul) and put the vitamin to test on myself. Read the article on Niacin on doctoryourself dot com. I eliminated arthritis from my fingers, increased libido, erections and quality of intercourse. Niacin is supposed to have great effects on mental conditions as well. It is used to help people break addictions to alcohol. Side effects include longer life (around 3 years added life expectancy) and flushing. I only use the flush niacin not the flush free niacin. The flush free niacin helps for some conditions but not for all. Especially it does not improve cholesterol (niacin lowers LDL or bad cholesterol and increases HDL).
I take around 500mg per day which is pretty low. Dr. Hoffer and others usually prescribed 1000 mg to 3000 mg daily. I believe in adjusting the dose to where you see results. I see results at 500mg, so I haven't gone much beyond that (some days I'll take 1000mg). Also, if you want to minimize or eliminate the flush, only take Niacin on a full stomach. On an empty stomach, the flush will be intense. Also, work yourself up to higher doses. Start with 50mg 3x per day and work up to 1000 mg per day.
If I could only take one supplement, it would definitely be Niacin. It is king in my opinion.