Minoxidil was originally used orally to treat high blood pressure (it is a vasodilatator) and hair growth appeared as a beneficial, unexpected side effect. That is why caution must be taken not to get too much of it into the bloodstream. Dermarolling very significantly increases the absorption of any skin products applied directly afterwards so you must be very careful and start slowly (do not apply too much after dermarolling at the beginning). If everything is fine, you can slowly increase it.
I suggest a regular 0.5 mm dermaroller in combination with 5% Minoxidil. Remember that I am not a MD and this is not medical advice. Minoxidil is a substance that can kill, when too much enters your body.
Related subject:
https://http://forums.owndoc.com/dermarolling-microneedling/dermarolling-for-thinning-hair/Topical minoxidil: cardiac effects in bald man.F H Leenen, D L Smith, and W P Unger
AbstractSystemic cardiovascular effects during chronic treatment with topical minoxidil vs placebo were evaluated using a double-blind, randomized design for two parallel groups (n = 20 for minoxidil, n = 15 for placebo). During 6 months of follow-up, blood pressure did not change, whereas minoxidil increased heart rate by 3-5 beats min-1. Compared with placebo, topical minoxidil caused significant increases in LV end-diastolic volume, in cardiac output (by 0.751 min-1) and in LV mass (by 5 g m-2). We conclude that in healthy subjects short-term use of topical minoxidil is likely not to be detrimental. However, safety needs to be established regarding ischaemic symptoms in patients with coronary artery disease as well as for the possible development of LV hypertrophy in healthy subjects during years of therapy.
J Am Acad Dermatol. 1987 Mar;16(3 Pt 2):677-85.
Safety and efficacy of topical minoxidil in the management of androgenetic alopecia.Rietschel RL, Duncan SH.
AbstractOf 149 subjects with androgenetic alopecia, 102 completed 1 year of a double-blind, randomized study comparing 2% minoxidil and 3% minoxidil solutions for safety and efficacy. One third of the subjects used a vehicle placebo for the first 4 months and then switched to 3% minoxidil. At 12 months the 2% minoxidil group switched to a 3% solution. During months 5 to 12 a steady increase in terminal hair counts occurred to an equal degree within the 2% and 3% minoxidil groups and the 3% treatment group switched from placebo. Total hair counts at 12 months increased from a baseline mean of 63.5 to 180.6 in the 2% treatment group, from 61.0 to 179.9 in the 3% group, and from 65.0 to 191.1 in the placebo to 3% crossover group. Although all 102 subjects completing 12 months of the study thought that visible hair growth had resulted, 89 were considered by the investigators to have visible growth. Dense hair growth, defined as hair long enough to cut or comb, was present in 48 subjects by their own evaluation and in 33 subjects by investigator evaluation. There were no serious side effects. Two instances of allergic contact dermatitis and four of pruritus were attributed to use of the drug. Two individuals complained of impotence, which disappeared within a few days of discontinuation of topical minoxidil. This effect has not been reported during the use of minoxidil in its oral form (Loniten) for the treatment of hypertension.