Question: What are the reported adverse effects of topical minoxidil?

Context:
Hypertrichosis is a well-recognized adverse effect of therapy with either oral or topical minoxidil.
reported increase of adverse events (additional hair growth on areas other than the scalp) with minoxidil (5%) twice daily. 
a case of central serous chorioretinopathy after application of topical minoxidil solution.
One month after the drug was discontinued, normal findings were found upon reexamination
The incidence of adverse effects such as pruritus or local irritation was similar in the 5% minoxidil group
The patients tolerated treatment with 1% topical minoxidil well without significant adverse effects.
An increased occurrence of pruritus, local irritation, and hypertrichosis was observed with 5% topical minoxidil versus 2% topical minoxidil and placebo.
Allergic contact dermatitis to topical minoxidil solution: etiology and treatment.
However, some patients present with complaints of pruritus and scaling of the scalp. The most common causes of these symptoms include irritant contact dermatitis, allergic contact dermatitis, or an exacerbation of seborrheic dermatitis. Patients suffering from allergic contact dermatitis may benefit from patch testing to determine the causative allergen. Among the patients we patch tested, propylene glycol was found to be the contactant in a majority of cases, not the minoxidil itself. 
A case of acute myocardial infarction associated with topical use of minoxidil (RiUP) for treatment of baldness.
A 45-year-old Japanese man with paroxysmal atrial fibrillation (AF) developed acute anteroseptal myocardial infarction (MI). He had used 1% topical minoxidil (RiUP) once a day for 4 months before the onset of MI for treatment of baldness.
Diffuse hypertrichosis during treatment with 5% topical minoxidil.
Five women affected by androgenetic alopecia developed severe hypertrichosis of the face and limbs after 2-3 months of treatment with 5% topical minoxidil. Minoxidil was discontinued and in all patients the hypertrichosis disappeared from the face and arms after 1-3 months, and from legs after 4-5 months
Generalized hypertrichosis after treatment with topical minoxidil.
hypertrichosis is uncommon after treatment with topical minoxidil for alopecia, and normally only occurs in areas close to the site of application. A 16-year-old girl is presented who developed generalized hypertrichosis 3 months after applying topical minoxidil for treatment of diffuse alopecia in doses greater than that prescribed
Two of our patients developed smoking intolerance during treatment with topical minoxidil for androgenital alopecia.
The relation between treatment with minoxidil and smoking intolerance was emphasized by stopping treatment and the disappearance of the smoking intolerance, and then by rechallenge in both patients. 
We observed an as yet unreported "polymyalgia syndrome" in four otherwise healthy males whose sole medication was topically applied minoxidil. They experienced fatigue, weight loss and severe pain in the shoulders and pelvic girdle, suggesting connective tissue disease. Three patients had a transient rise in liver enzymes, while other laboratory analyses remained normal. Tritanomaly was detected in two patients who underwent systematic color vision testing. All symptoms disappeared after withdrawal of minoxidil. Rechallenge was positive once in one patient and twice in another. 
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.
The most frequently reported adverse reactions are mild scalp dryness and irritation and, rarely, allergic contact dermatitis.
Eight deaths that occurred during Upjohn-sponsored clinical trials of topical minoxidil and two deaths in subjects who used extemporaneous formulations of the drug are summarized. Of the eight patients in clinical trials, five had cardiovascular abnormalities and two had acquired immunodeficiency syndrome-related pneumonia. One patient died of a self-inflicted gunshot wound. One of the subjects who was using extemporaneous topical minoxidil had hypertension and arteriosclerotic disease and the other died of a myocardial infarction. There is little likelihood of significant adverse effects attributable to topical minoxidil because of its low systemic absorption. The evidence suggests that these deaths were the result of causes other than use of the drug.
Only 2% of prescribers reported complications other than local irritation that they associated with topical minoxidil therapy, but underreporting of noncutaneous side effects in this survey of dermatologists cannot be excluded.
Typical side effects of this topical treatment include irritative dermatitis going along with pruritus, erythema, scaling and dryness, which occur especially at the onset of the therapy. In some cases, allergic contact dermatitis or exacerbation of seborrheic dermatitis has been reported. While most of the patients with allergic contact dermatitis described in the literature showed a positive sensitization to the vehicle substance propylene glycol evaluated by patch testing, reactions to the active ingredient minoxidil are rare

Answer: Typical side effects of this topical treatment include irritative dermatitis going along with pruritus, erythema, scaling and dryness, which occur especially at the onset of the therapy. In some cases, allergic contact dermatitis or exacerbation of seborrheic dermatitis has been reported.
Hypertrichosis is a well-recognized adverse effect of therapy with either oral or topical minoxidil.
We observed an as yet unreported "polymyalgia syndrome" in four otherwise healthy males whose sole medication was topically applied minoxidil. They experienced fatigue, weight loss and severe pain in the shoulders and pelvic girdle, suggesting connective tissue disease. Three patients had a transient rise in liver enzymes, while other laboratory analyses remained normal. Tritanomaly was detected in two patients who underwent systematic color vision testing.
A case of central serous chorioretinopathy after application of topical minoxidil solution.
A case of acute myocardial infarction associated with topical use of minoxidil (RiUP) for treatment of baldness.
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).
Two of our patients developed smoking intolerance during treatment with topical minoxidil for androgenital alopecia.