Brief Answer: Reaction to drug, if appeared after taking drug Detailed Answer: Hi and thanks for the query, It is important to know if you only experienced the dark spots after using the Magnesium. The speed at which the dark spots appeared is also important to be known. IN case you experienced these spots only after using the drug, and also considering the fact that the spots are associated with itches, It is very probable that this reaction was from use of Lactated magnesium. It is advisable to stop the drug, consult a doctor for the prescription of an appropriate topical anti inflammatory agent or topical steroid, and an anti histaminic drug in case of severe itches. My opinion would be going off the drug, consulting your doctor for a complete review and management of side effects. Your doctor, considering your medical history and peculiarities would be able to prescribe an appropriate substitute. Please do feel free asking further questions in case you have any specific concerns. I would be glad making my humble contribution to your well being. Thanks and kind regards. Dr Bain

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