Is it safe to use Minoxidil 5% on healthy hair?

Minoxidil is effective when it is in use. When you quit you usually loose the hair gained through minoxidil use. It is better to consult with your doctor before using it.

Minoxidil is a FDA-approved topical medication for hair growth that works well for androgen (hormone) related hair loss.  It helps extend the growth cycle of hair and
decrease shedding that naturally occurs. 
For minoxidil to work, there is an activation process.  During the first four weeks, fine hairs may
shed where thicker hairs may replace. 
During this time, it may appear you are losing hair when it is actually
working.  However, if you stop using
minoxidil, your hair will revert back to the same growth cycle.  I recommend a consultation with an expert
in hair restoration. 

It is normal to shed hair every day.  It is estimated that you will loose 100 hair each day normally.  You could try counting the hair you are shedding.  There is another test that will tell you if you are starting to thin.  This is a cross sectional trichometry comparing the back of your head with the top of your head.  If both numbers are similar, you are not likely thinning and you will not benefit from minoxidil.  There are some considerations however.  All hair in all men and women begins to age with time beginning at age 35.  Things like Wnt-act, and Haircycle products can help you maintain a more youthful microenviroment for you hair and help keep the hair in place over time.  If you are loosing your hair, you might consider medications like minoxidil, but you first need to understand if you are naturally aging or whether you have androgenic alopecia.  

I suggest seeing a hair loss expert now to go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone which can help with hair regrowth and/or hair transplantation. See an expert. Best, Dr. Emer

I suggest you consult a practice who can evaluate you for miniaturization with high magnification hair photos.  If you see some thinning of the hairs you can consider using it, but it is not without risks or complications.  Dermatitis is not uncommon from the preservatives in it.  I've seen people even loose (albeit temporarily) all their hair from minoxidil products.  Good luck!  Dr. Rome

While minoxidil works for some, the
problem with the medicine is that it does not stop hair loss, and the
DHT will continue is binding to the hair shaft which will eventually
overtake any additional growth caused by the Minoxidil and die, perhaps
just slightly later than it would have without the medicine.

Also, the alcohol base required to support the active ingredients also cause irritation of
the scalp and sever reactions for many people.
The best thing to do would be to see a doctor who specializes in
hair regrowth and the rebalancing of body biochemistry who can diagnose the cause and severity of your hair loss. From there, you can find a proper way to treat it.

If your hair for the most part looks fine, it's unlikely minoxidil is the right choice for you. However, I'd recommend you speak with a physician who specializes in hair loss to confirm this. Minoxidil should not be used on normal, healthy hair.  Anyone who feels they are shedding quite bit needs a comprehensive evaluation including blood tests. 

minoxidil is a drug so why would you take it if you don't have a problem with hair loss. There are side effects of this drug including a hair addiction to new hairs grown by it.

If you are thinking of using any medical treatment options for your hair loss, it is best to do it under the supervision of a hair loss specialist. Usally in mu experience, minoxidil causes dryness of scalp.