Is it permissible to sell medicine at its new price after it has increased in the market, knowing that it was purchased at an old price?

There is no objection to selling medicine at its new price, for Allah Almighty has permitted buying, selling, and profit. There is no specific limit on profit in Islamic law unless it reaches the point of greed and exploitation of the poor's needs. Leniency in buying and selling is encouraged. However, if you inform the buyer of the price at which you purchased the medicine, then truthfulness is obligatory, because a sale can either be a negotiation where it is not necessary to inform the buyer of the original price, or a trust sale where it is necessary to disclose the original price, such as Murabaha, Tawliyah, and Wadi'ah sales.