Is there a pill that substitutes for Rogaine?

You are correct. Oral minoxidil has risks ... but so does every oral medication for male balding (finasteride and dutasteride). In general, the most effective oral treatments have the most potential side effects. The least effective treatments have the fewest side effects. 

Thank you for your question.  Scalp itching and dandruff are not an uncommon side effect with the liquid form of Rogaine.  I find that many of my patients who experience these side effects often do much better when the switch to the foam formulation.
It's important to note that there are a variety of reasons we can start losing our hair, and the treatments can differ depending on the exact reason.  Assuming you are experiencing genetic/age-related hair loss, there are a number of oral medications that can help as well - Propecia is FDA-approved to treat male pattern hair loss, while some women with female pattern hair loss can benefit from spironolactone.  I generally do not recommend the oral form of minoxidil for the reasons you mentioned.  I would recommend scheduling a consultation with a board-certified dermatologist to discuss your hair loss and treatment options. 

Yes, minoxidil can be taken in a pill form.  It requires that a doctor discusses and prescribes this medication so that you understand the potential side effects and risks