The only study that directly compared oral with topical was for FPH but again proves that oral is better even at a very low dose
After 24 weeks of treatment, the total hair density increased by 12% (95% confidence interval [CI] 8.0%-16.1%) in women taking oral minoxidil and 7.2% (95% CI 1.5%-12.9%) in women applying topical minoxidil
Minoxidil 1 mg oral versus minoxidil 5% topical solution for the treatment of female-pattern hair loss: A randomized clinical trial
After 24 weeks of treatment, the total hair density increased by 12% (95% confidence interval [CI] 8.0%-16.1%) in women taking oral minoxidil and 7.2% (95% CI 1.5%-12.9%) in women applying topical minoxidil