I've been using a very fine needle derma roller prior to my nighty application of Rogaine Foam. I'm certain the absorption rate has increased significantly. My concern is with the increased risk for side effects. If I'm using the derma roller and applying a significant amount of Rogaine Foam to the entire top of my scalp, what are my chances of suffering some of the more serious side effects especially the cardiac related issues? Here's what I've read recently...

Side Effects by Body System

General

Minoxidil topical is generally well tolerated. Dermatological adverse events are the only side effects reported more commonly as compared to placebo.

Cardiovascular
Edema, salt and water retention, pericardial effusion, pericarditis, tamponade, tachycardia, and angina have been reported with oral minoxidil. Patients with underlying heart disease may be at increased risk for these or other cardiovascular adverse effects.

Rarely, cardiovascular side effects have included edema, chest pain, blood pressure changes, palpitations, and changes in pulse rate with minoxidil topical therapy.

Local
Despite low levels of systemic absorption, in one study of 35 men using either topical minoxidil 2% twice a day or placebo for 6 months, minoxidil was associated with cardiac changes, such as significant increases in left ventricular end-diastolic volume, cardiac output, and left ventricular mass.

Systemic side effects are uncommon since very little minoxidil is absorbed after topical application. In one study, the serum levels after 2.5 mg twice a day oral versus 2% twice a day topical minoxidil were 32.8 and 1.7 ng per mL, respectively.

Exacerbation of hair loss/alopecia has been reported.