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The difference between Minoxidil
2% and 5% is of the concentration or the strength.Both are used and have good effect but it is always better to start with 2%. Minoxidil causes dilation of the blood vessels and opens the hair follicle for hair to grow so in some people due to dilatation of bood vesses of head it can give rise to headache or you can have lightheadedness
.It is better to start with 2% and once it is well tolerated you can increase the strength to 5%.