Why is Minoxidil causing my muscles and tendons to hurt?

This needs an in-person evaluation. I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

Thank you for your question! If you believe that you are having muscle pain from minoxidil, then stop using it.  Make sure that the symptoms go away and that will confirm the relationship. There is no harm from stopping minoxidil for a week or two. Best of luck!

Headaches can certainly occur with minoxidil. However muscle pain and tendon issues are not common. Minoxidil has minimal effects on skeletal muscle, in contrast to effects on vascular smooth muscle and cardiac tissue. However if worried be sure to see a physician and be sure to stop minoxidil. Your physician will advise if restarting a trial of minoxidil is appropriate or not (ie drug rechallenge). Headaches go away quickly when minoxidil is stopped.

Even though it is the first time I hear of this adverse effect, it can still be an idiosyncratic reaction.\First try to establish the relationship by stopping the drug for some days and re-starting and seeing whether symptoms follow these changes.
Then try to change into foam if you are using lotion or vice versa.
Then you can try another Minoxidil brand, maybe it can help.

If you believe that you are having muscle pain from minoxidil, then stop using it.  Make sure that the symptoms go away and that will confirm the relationship. There is no harm from stopping minoxidil for a week or two