I have used 5,000 mcg synthetic biotin for many years to help my hair and nails. My nails have always been thin, weak always splitting. Since taking this naturally sourced biotin by FutureBiotics my nails grow quickly and are strong! it doesn't take long to see the results. I ran out and started using the synthetic kind again and my nails got very weak again. I only take 1/3 to 1/2 of the recommended dosage too because it is naturally sourced I find I need less.